School of Civil Engineering

School of Civil Engineering
Highway Traffic and Safety Analyses Types of Traffic Studies Purdue University School of Civil Engineering West Lafayette

What Answers Are Sought?
Current highway and parking use Current traffic characteristics Current traffic and parking quality Current highway safety How to improve current traffic conditions Impact of new highway projects/improvements Impact of a new land development Future traffic conditions (limited change in traffic pattern)

Scale of the Studies Single facilities (intersection, road section)
Arterial streets Corridors (several parallel roads) Local areas (part of the network) Entire systems (city, county, state)

Traditional Traffic Studies (according to McShane et al.)
Volume studies Speed studies Travel time studies Delay studies Density studies Headway and spacing studies Accident studies (classified by McShane et al. as a special study)

Special Traffic Studies and Analyses
Location studies Traffic impact studies and analyses Safety analyses Identification of hazardous locations Identification of hazard sources Identification of countermeasures Corridor studies Parking studies Congestion analyses Pedestrian studies Before-and-after studies

Who Are Traffic Engineers’ Clients?
Policy makers Highway administration State County City Citizens groups Land developers Business owners

Example Studies Wal-Mart study in Centerville (Utah)

Traffic Studies and Analyses offered by HIGGINS ASSOCIATES, CA ( Access & Circulation Studies Accident Analysis Freeway Operations Analysis Speed Studies Traffic Count Programs Traffic Handling for Special Events Traffic Impact Studies Traffic Operations Studies Traffic Safety Studies Traffic Signal Operations & Timing

HIGGINS ASSOCIATES, CA (http://www.kbhiggins.com/traffic.html)
Scotts Valley Drive, City of Scotts Valley Performed detailed traffic data collection including video tapes, measurement of delay, residual queues and travel times for a three intersection interchange signal system. Optimized cycle lengths, phase sequences and splits, and implemented in the field with Caltrans staff. Documented optimized traffic operations and noted improvements in delay and queue lengths. The optimization was performed using Synchro 3 and TSPPD (Time Space Platoon Progression Diagram). Morgan Hill On-Call Municipal Traffic Engineering Services Responded to citizen complaints. Performed warrant analyses for requested traffic control devices throughout the City. Provided site plan review. Performed signing, striping and signal design.

Highway Traffic and Safety Analyses Lecture 3: Traffic Impact Analysis (1) Purdue University School of Civil Engineering West Lafayette

The Case of Potawatomi Bingo and Casino Parlor Expansion

Traffic Impact Analysis (1)
Warrants for analysis Review process Issues addressed by traffic impact studies Extent of study Study area Time horizon and period of analysis Data needed

Warrants for Traffic Impact Analysis
Example cases when an impact analysis may be needed: Zoning/rezoning Land subdivision Site plan approval Building permit Amendments to a long-term plan Permit for major driveways

Criteria may be locally established based on: trip generation, development or area characteristics, or localized conditions. Recommended criterion in lieu of local criteria: 100 or more added vehicle trips in the peak direction (inbound/outbound) during the site’s peak hour traffic

Example criteria for warrants: Number of peak hour trips Number of daily trips Amount of acreage to rezone Number of dwelling units or square footage in the project Project in a sensitive area

Review Process Parties involved
Developer (land owner, business owner) Reviewer (local, state transportation agency) Preparer (consulting company) Early and open discussion between the three parties is important

Review Process Objectives Mutual understanding Realistic awareness
Objectiveness of the review Fair assessment of impacts Identification of truly needed improvements

Issues to Address in Analysis
Required extent of analysis Needed guidelines and manuals Study area Time horizon and period of analysis Needed data Techniques for data collection and analysis Target level of service Isolating the studied traffic impact from other impacts Needed traffic improvements Phasing improvements Changes needed in the project (development) Documentation

Required Analysis Extent
Which components of the site impact studies are needed? How detail should the analysis be? How large should a study area be? How long and how many time horizons are needed? Is field data collection needed? Should any adjacent development be considered? Should planned highway improvements be accounted for? Are safety, sigh distance, queuing and other analyses needed?

Needed Guidelines and Manuals
Guidelines for access/traffic analysis Trip generation Manual of traffic engineering studies HCM MUTCD Traffic engineering software manuals Safety analysis guidelines (future HSM)

Study Area The Study Area must include the Impact Area
Each impact analysis includes all site access points and major intersections adjacent to the site Additional area may be included based on local or site specific issues (for example, congested locations with additional traffic generated by the project) Excessively large area increases costs of analysis

Time Horizon Development Suggested Analysis Horizons
< 500 peak-hour trips, single-phase development Opening year with full build-out and occupancy assumed peak-hour trips, single phase development Five years after opening date >1000 peak-hour trips, single phase development Adopted transportation plan horizon year (if diversion from the plan) >500, multiple-phase development Opening years of each phase Year with complete build-out and occupancy Five years after year of complete build-out and occupancy

Period of Analysis Seasonal, weekly, and daily volumes variations
Design volume (20-40th highest hourly volume) Approximation of the design hour Available volume data vs. own counts Average day vs. “design day” Background traffic vs. on-site generated traffic Adjustment factors Worst 15-minutes in the design hour

Useful Traffic and Crash Data
Recent and historical daily and hourly volume counts (Figure 3-1) Recent intersection turning movement counts (Figure 3-2) Volume variation adjustment factors Projected volumes from previous studies and regional plans Origin-destination or trip distribution data Accident statistics where safety problems are anticipated (three years)

Useful Land Use Data Current land use, densities, and occupancy
Approved development projects and planned completion dates Anticipated development of other parcels Land use master plan Zoning in vicinity Current and future population and employment by traffic analysis zone (for site traffic distribution)

Useful Infrastructure Data
Current street characteristics (direction of flows, number of lanes, right of way, access control, traffic control) (Figure 3-3) Roadway functional classification Traffic signal locations, coordination, timing Adopted local and regional plans Transit service and usage Pedestrian and bicycles linkage and usage Parking facilities

Figure 3-1 Current Daily Traffic Counts
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Figure 3-2 Turning Movement Counts
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Figure 3-3 Infrastructure Data
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Highway Traffic and Safety Analyses
Lecture 4: Traffic Impact Analysis (2) Purdue University School of Civil Engineering West Lafayette

Lecture Outline Traffic in the study area
Methods of traffic forecasting Network modeling Trends method Growth rate method Traffic generation method Pass-by trips Analogy method - own data collection

Traffic in the Study Area Future
Analysis Area Study Area Future Background Traffic Analyzed Site Future Generated Traffic

Methods of Traffic Forecasting
Large projects Network traffic modeling Small projects – Background traffic Trends method, or Growth factor method Generated traffic ITE trip generation tables, or Analogy method

Network Traffic Modeling Large Projects

Network Traffic Modeling Large Projects
Transportation planning studies Rather crude representation of networks May be appropriate for large projects Interpolation possible if the planning and study horizons are different (see Figure) Possible discrepancies between the plan assumptions and the land use and street system in the study horizon year Adjustments to bring details may be needed Network modeling for the impact study should be considered (QRS)

Trends Method Background Traffic for Small Projects
ADT or Hourly Volume Rate Now Year

Growth Rate (Factor) Method Background Traffic for Small Projects
Future Volume = Past Volume · (1 + Growth Rate)N where N = Future Year – Past Year Example: 1,200 veh/h in 2000, 3% growth rate Volume in 2004 = 1,200 · ( ) = 1,350 veh/h

ITE Trip Generation Tables Generated Traffic for Small Projects

ITE Trip Generation Tables Generated Traffic for Small Projects
General Office Building (710) ITE Trip Generation Tables Generated Traffic for Small Projects

ITE Trip Generation Tables
Equations vs. rates When using rates, use average with local adjustments Weekday, weekend, vs. peak hour (see Table) Select the best descriptor (development unit) Involved uncertainty Limitations: suburban, only cars, national averages, single developments, diverted trips, pass-by trips

Pass-by Trips No new development 1,000 veh/h
Predicted driveway traffic = 550 trip ends/h (ITE tables) New development Primary traffic generated Pass-by traffic (320 trip ends/h) 1,000 veh/h (160 vehicles stop by) Primary traffic generated = 550 – 320 = 230 trip ends/h

Pass-by Trips For shopping centers, weekday, PM peak (ITE, 1991)
ln(p) = ·ln(x) R2=0.34 where p is the percent of the driveway traffic volume which is the pass-by traffic.

Pass-by Trips Estimate the primary traffic generated by a shopping center and added to the background traffic during the weekday PM peak. The gross area of the shopping center is 120,000 ft2. The traffic entering and exiting the center is 450 veh/h. Calculations: ln(p) = ·ln(120) = 3.74, p = 42 % Primary traffic = (1 – 42/100)·450 = 260 veh/h

Analogy Method – Own Data Collection Generated Traffic for Small Projects
Select generators with similar characteristics Daily machine counts for at least three days Period with peak hour counts during “design days” Manual counts can be used to adjust machine counts Interviews with travelers, O-D counts techniques (primary vs. pass-by trip ends) Interviews with the site owner or manager (development characteristics, occupancy level, etc.) Submit data to the ITE using special forms

Typical Peak Hours Land Use Typical Peak Hours Peak Direction
Residential 7-9 am weekdays Outbound 4-6 pm weekdays Inbound Regional Shopping 5-6 pm weekdays Total 12:30-1:30 Saturdays 2:30-3:30 Saturdays Office Industrial Varies with employee shift schedule Recreational Varies with type of activity Back

Interpolation to Use Forecasts of Planning Studies
ADT Impact Study Horizon Planning Study Horizon Now Year Back

Highway Traffic and Safety Analyses Lecture 5: Traffic Distribution and Assignment in Impact Analyses Purdue University School of Civil Engineering West Lafayette

Lecture Outline Four-step traffic network modeling (large projects)
Traffic forecast task for small and medium projects Trip distribution Analogy method Crude gravity method Traffic assignment to routes Non-car trips (pedestrians, bikes, public transit)

Four-Step Traffic Network Modeling (Large Projects)

Traffic Forecast Task for Medium and Small Projects
Background traffic (car and non-car) Trends or growth factor methods Traffic already assigned New developments (analyzed one and other) Trip generation tables Car trips only How to distribute, and assign car traffic generated by new developments? What about non-car trips?

Traffic Forecast Task for Medium and Small Projects
1 2 3 4 5 Impact Area (Study Area)

Traffic Distribution Judgment (most popular) Analogy method
1 2 3 Traffic Distribution Judgment (most popular) Analogy method Crude gravity method

Analogy Method Existing similar development
Near the proposed development Data collection techniques License plate technique Driver response survey

Market Area System Area Market Area Development Site Impact Area
More than 80% of trips System Area

Market Area

Market Area Market Area Impact Area 12,000 trip ends/day

Gravity Method 1 3 2 where: Tij= number of trip from zone i to zone j,
1 2 3 where: Tij= number of trip from zone i to zone j, Pi = trip production in zone i, Aj = trip attraction in zone j, Fij = inverse function of travel time from i to j, Kij = adjustment factors for flow Tij.

Crude Gravity Method where: Tij = trips between zones i and j,
1 2 3 where: Tij = trips between zones i and j, P0 = outbound trips from the new development, A0 = inbound trips to the new development, Sj = relevant socioeconomic characteristic of zone j in the market area.

Crude Gravity Method Market Area Impact Area 6,000 population
5,000 work places 6,000 population 1,000 work places 3,000 population no work places Impact Area

Crude Gravity Method 2,000 outbound trips/day 0 % 16 % Impact Area
84 % 16 % 0 % 320 1,680 3,000 population no work places 6,000 population 1,000 work places Impact Area 1,000 population no work places 10,000 population 5,000 work places Residential development

Crude Gravity Method 2,000 outbound trips/day 15 % 30 % 5 %
50 % 30 % 15 % 5 % 600 300 1,000 100 3,000 population no work places 6,000 population 1,000 work places Impact Area 1,000 population no work places 10,000 population 5,000 work places Office building

Trip Distribution (daily)
50% 35%

Route Assignment

Route Assignment Judgment (most popular) Simplified logit method

Trip Assignment Logit Method
Utility of route U = function of route length, travel time, trip cost, etc. Example: U = x travel time in minutes (just an example) Two routes, L1 = 1.5 mi, V1 = 30 mi/h, L2 = 2.0 mi, V2 = 35 mi/h. U1 = -1.50, U2 = -1.71

Trip Assignment Logit Method
Logit equation where: Pi = proportion of travelers using route i, Ui = utility of route i. Example: U1 = -1.50, U2 = -1.71, In the all-or-nothing method, all the trips are assigned to the best route.

Example Traffic Forecast (format important!)
230 = traffic generated by the development (500) = total traffic Example Traffic Forecast (format important!)

Non-car Trips Judgment Analogy method Logit method

Lecture 6: Traffic Volume Variability and Studies Purdue University School of Civil Engineering West Lafayette

Lecture Outline Definitions Volumes variability Estimation of AADT
Design volume Counting techniques Types of volume studies

Definitions Count – number of vehicles/travelers passing a highway spot in a counting period Volume – number of vehicles/travelers passing a highway spot per unit time Capacity – maximum and repeatable volume of vehicles/travelers Demand – volume not influenced by highway capacity

Definitions Capacity Demand Traffic Intensity Volume Congestion Time

Definitions Volume Traffic Intensity Time

AADT vs. ADT AADT = Annual Average Daily Traffic (veh/day)
ADT = Average Daily Traffic (veh/day) represents periods other than a year Weekly ADT, Monthly ADT

Seasonal Variability of Monthly ADT
128 % Counts in August on a rural road have given August Monthly ADT = 10,000 veh/h What is Annual ADT? AADT = 10,000∙(1/1.28) =10,000∙0.781 AADT = 7,810 veh/day 0.781 = Seasonal Factor (SF)

Weekly Variability of Daily Volumes
0.158 Thursday daily traffic on a suburban arterial = 30,000 veh/day Weekly ADT = ? = 30,000∙(1/0.158/7) = = 30,000∙0.904 = Weekly ADT = 27,100 veh/day 0.904 = Weekly Factor (WF) Weekly ADT ≈ Monthly ADT

Seasonal and Weekly Variability of Daily Volumes
Counts in average weekday in March, recreational road, in Minnesota, March Weekday ADT = 20,000 veh/day AADT=? AADT = 20,000∙(1/0.80) = 20,000∙1.25 AADT = 25,000 veh/day 1.25 = WF∙SF

Daily Variability of Hourly Traffic
Vehicle counts on a local road on Wednesday between 4-7 PM gave total 2,350 vehicles Wednesday ADT = ? Counting Hour Percent of Daily Traffic Total Wednesday ADT = 2,350∙(1/0.251) = 2,350∙3.98 = 9,360 veh/h 3.98 = Daily Factor (DF)

AADT Estimation with Short Counts
AADT = V·DF·WF∙SF where: AADT = Annual Average Daily Traffic, V = count in veh, DF = Daily Factor, WF = Weekly Factor, SF = Seasonal Factor, More than one day of counting (three days) and extended count periods each day are recommended

Day-to-day Variability of Daily Profile
95% of volumes

Within-Week Variability of Daily Flow Composition

AADT Estimation - Exercise
Vehicle counts have been conducted in mid March on Thursday between 3 and 5 PM. Known: Total count V=2,000 veh, Volume between 3 and 4 PM equals 6 % of daily traffic Volume between 4 and 5 PM equals 7 % of daily traffic Thursday daily traffic equals 16 % of weekly traffic March daily traffic equals 98 % of AADT Calculate Daily Factor DF Weekly Factor WF Seasonal Factor SF AADT

AADT Estimation - Exercise
DF DF = 1/(Proportion of Daily Traffic) DF = 1/( ) = 7.69 WF WF = 1/(Proportion of Weekly Traffic)/7 WF = 1/0.16/7 = 0.89 SF SF = 1/(Proportion of AADT) SF = 1/0.98 = 1.02 AADT AADT = V·DF·WF∙SF V = 2,000 vehicles AADT = 2,000∙7.69·0.89·1.02 = 13,800 veh/day

Design Volume Definition
K 30

Design Volume Estimation Using Factor K
DHV = AADT·K·D AADT in the horizon year (veh/day) K = proportion of AADT during the 30th rank hour (other ranks may be used too) D = directional split (busier direction)

Design Volume Estimation Using Factor K

Alternative Estimation of Design Volume
Estimate AADT1 for the year with available vehicle counts, AADT1=V∙DF1∙WF1∙SF1 Predict AADT2 for the future year using a growth factor AADT2=AADT1∙GF Select month, day of week, and hour in the future year when the volume is likely to be close to the design volume Convert the predicted AADT2 to the hourly volume for the hour selected in step 3, DHV=AADT2/DF2/WF2/SF2 or DHV = V ∙ (DF1/DF2) ∙ (WF1/WF2) ∙ (SF1/SF2) ∙ GF

Short-Term Volume Variability
Traffic performance is checked for the worst 15 minutes of the design hour

Peak Hour Factor Estimation of PHF
PHF = Hourly Count/(4·Highest 15-min Count) Use of PHF Peak Volume Rate = DHV/PHF

Types of Volume Studies
Intersection counts (duration depends on the purpose, 15-minute intervals or shorter, turning volumes) Pedestrian counts (duration depends on the purpose, 5-minute intervals or longer) Cordon counts (one weekday + travelers’ survey) Screen line counts (hourly counts for a weekday) Area wide counts Control counts (hourly counts with permanent stations) Coverage counts (hourly counts for one or two days)

Counting Techniques Manual counting Machine counting
For one day or less Turning volumes, pedestrians, test counts Pencil and paper Electronic manual recorders Machine counting For longer counting periods: one day or longer Permanent stations (inductive loops, WIM) Portable stations (pneumatic, inductive, magnetic, video, etc.)

Origin-Destination Studies
External (on the road) Cordon studies Roadside interviews Postcard studies License plate studies Tag-on vehicle method Lights-on studies Transit passenger questionnaire

Origin-Destination Studies
Internal (off the road) Dwelling unit interviews Vehicle owner mail questionnaires Interview at traffic generators (workplace, etc) Truck and taxi surveys

Lecture 7: Parking Studies
Highway Traffic and Safety Analyses Lecture 7: Parking Studies Purdue University School of Civil Engineering West Lafayette

Lecture Outline Definitions Demand vs. Supply Parking Inventory
Accumulation Studies License Plate Checks

Definitions Parking volume (veh/day) Parking accumulation (veh)
Number of vehicles parking in a study area during a specific length of time (typically a day). Vehicles leaving the parking area and returning are counted twice. Parking accumulation (veh) Number of vehicles parking at a specific time Parking accumulation curve A curve showing variation of parking accumulation over time

Definitions Parking load (veh-hour) Parking duration (hour)
The area under the parking accumulation curve Parking duration (hour) Average parking time Parking turnover (veh/space) Number of vehicles per parking space during the analyzed period

Accumulation Curve Accumulation (veh) Time (hrs)

Demand vs. Supply Maximum Demand No. of Legal Spots Accumulation (veh)
Time (hrs) Accumulation (veh) No. of Legal Spots True Demand

Demand vs. Supply Hidden Demand Accumulation (veh) Illegal Parking
Time (hrs) Accumulation (veh) Hidden Demand Illegal Parking

Parking Inventory Number of parking spaces
Time limits and hours of operation Type of ownership Rates and method of fee collection Parking regulations at curb spaces (loading zones, passenger zones, handicapped zones, taxi zones, bus zones) Lot or garage Degree of permanency

Parking Inventory Numbering System
Curb Face Number 1 2 4 3 Block Number 6 7 5 6 7 5 Off-Street Facility Number

Parking Inventory Summary Sheet
6 5 1 2 4 3 7 Block Number Curb Face Number Off-Street Facility Number Parking Inventory Summary Sheet Block Facility Inventory Data Parking Spaces Non-public Spaces Data 3 Data 4 Data 5 ….. 5 1 7 2 12 3 6 4

Area and Time of Parking Accumulation Studies
Study area – parking area for the studied development On days when maximum parking is expected Counting period should include time of intense parking 6 AM to 8 PM for employment and commercial sites (several times) 1 AM to 5 AM should be covered in residential areas (once)

Techniques of Parking Demand Studies
Cordon-based without vehicles identification Cordon-based with vehicles identification Route-based without vehicles identification Route-based with vehicles identification

Cordon-Based Parking Study without Vehicles Identification
Estimating the initial accumulation by counting along routes Continuous counting of vehicles entering and exiting the study area Estimating the final accumulation by counting along routes

Cordon-Based Parking Study with Vehicles Identification
Estimating the initial accumulation by counting along routes Manual recording of license numbers when low flows Videotaping of license numbers with post-processing when large flows Estimating the final accumulation by counting along routes

Route-Based Accumulation Studies without Vehicles Identification
Counting along a pre-specified route that covers the study area Careful routes design for large areas (multiple field checkers) Counting vehicles or empty spaces (what easier) Counting interval: one or two hours 5-hour shifts Common starting point helps supervising

Route-Based Accumulation Studies with Vehicles Identification
Hand-held computers, tape recorders, or paper worksheets Counting interval: 1/3 of the average parking duration and not longer than 1-2 hours 1 ½ minutes per one parking space needed 5-hour shifts Careful routes design for large areas (multiple field checkers) Common starting point helps supervising

Exercise 1 Parking vehicles were counted every two hours
Draw a parking accumulation curve, calculate the parking load based on the parking counts.

License Plate Checks Calculations
Turnover = Parking Volume/Parking Spaces Parking Load = Av. Accumulation x No. of Intervals x Av. Interval Average Parking Duration = Parking Load/Parking Volume

Exercise 2 The license plates were noted every two hours.
Determine the parking volume and calculate the parking turnover and the average parking duration.

Results Obtainable from Various Parking Study Techniques
Cordon without Identification Cordon with Identification Routes without Identification Routes with Identification Accumulation Yes Volume No Turnover Average Duration Variability of Duration Space use Illegal parking Yes/No Enforcement

Lecture 8: Speed, Travel Time, and Delay Studies
Highway Traffic and Safety Analyses Lecture 8: Speed, Travel Time, and Delay Studies Purdue University School of Civil Engineering West Lafayette

Outline Speed Travel time Delay Definitions Study applications
Measurement techniques Measurement issues Data analysis Travel time Applications Delay

Definitions Spot speed – a speed of a vehicle at a spot (instantaneous speed) Space-mean speed – an average instantaneous speed of vehicles that occupy a highway segment Time-mean speed – an average instantaneous speed of vehicles passing a spot during a period

Definitions Free-flow speed – vehicle speed when other vehicles do not impede Running speed – vehicle speed not influenced by intersections and other spot obstructions Travel speed – average speed along a highway segment

Applications Traffic operations and control
speed limits, advisory speeds, critical speeds, no-passing zones, signs location, signals design Advanced Traveler Information Systems Houston San Diego Highway design Highway safety Speed trends Indiana (p.37 and following) Effectiveness of controls and programs

Measurement Techniques
Manual Vehicle detectors Radar

Bias in Radar Measurements
Vehicle  Radar beam True Speeds (mph) Angle  (o) Measured Speeds (mph)

Sample Size Determination
Test measurements Estimation of required size based on the test results N = (S·K/E)2 where: N = minimum number of required speed observations, S = speed standard deviation estimated from test sample, E = permitted error in mean speed estimate, for example, E = 5 mi/h, K = depends on desired confidence level and size of test sample, Test sample larger than 30 → K = 1.96 for 95% confidence (standardized normal distribution), Test sample 30 or smaller → K = varies with the test sample size and confidence level (Student-t distribution). Additional measurements if required

Sample Size -Example Initial measurements gave speeds: 45, 41, 32, 50, 49, 35 (mph). How many more speeds are required if the permitted error is 3 mph at the level of confidence 95%? Mean = ( )/6 = 42.0 mph S2 = [( )2+( )2+…]/(6-1) = 54.4, standard deviation S = 7.4 mph K = 2.57 for sample size with dof = 6-1 = 5 and the 95% confidence interval N = (S·K/E)2 N = (7.4x2.57/3)2 = 40.2 Additional =35 speed observations are required Using normal distribution would give = 18 additional speeds

Frequency distribution table for set of speed data
Data Analysis Frequency distribution table for set of speed data

Data Analysis

TRAVEL TIME

Definitions Travel time – time taken to travel a highway segment
Running time – travel time along a highway segment without spot obstructions (intersections) Free-flow travel time – travel time along a highway segment without impedance from other vehicles Desired travel time – travel time along a highway segment without spot obstructions nor impedance from other vehicles

Study Applications Identify problem locations
Input to traffic assignment models Input to economic analysis Congestion management Component of delay studies Travel time contour maps (accessibility vs. mobility)

Travel Time Contour Maps

Probe vehicle Manual technique Automatic technique License plate method

Travel Time Measurements
1st Street 2nd Street 3rd Street Travel Time Travel Distance Vehicle Trajectory Running Speed Running Time

Definitions Delay - unwanted extra travel time
Delay = Travel Time – Desired Travel Time Operational delay - delay caused by impedance from other vehicles Operational delay = Travel Time – Free-Flow Travel Time Control delay - delay caused by traffic control Control Delay = Travel Time – Running Time

Study Applications Identification of problem locations
Evaluation of improvements Input to planning and economic analyses Trend analysis

Based on travel time measurements Based on queue measurements (control delays)

Delay Measurement Based on Travel Times
1st Street 2nd Street 3rd Street Control Delay Travel Time Vehicle Trajectory Running Time Travel Distance

Delay Measurement Based on Queues
Total counts = = 371 vehicles Volume = 530 veh/15 min Average stopped delay = 371 x 15 / 530 = 10.5 sec Additional adjustments are required to incorporate the deceleration/acceleration component

Highway Traffic and Safety Analyses Lecture 9: Highway Capacity Manual 2000 (original presentation by R. Dowling revised and expanded by A. Tarko) Purdue University School of Civil Engineering West Lafayette

Lecture Objectives To highlight the content of the Year 2000 edition of the Highway Capacity Manual. To help identify suitable procedures in the Manual things and properly apply to traffic operations problems. This seminar has two objectives: 1. To highlight the content and major changes of the Year 2000 edition of the Highway Capacity Manual, and 2. At the end of the seminar attendees will know: Where to find material in the HCM, How to apply the HCM to traffic operations problems, The major changes in methodology between the 1994, 1997, and 2000 HCM

Purpose of the HCM “To provide transportation practitioners and researchers with a consistent system of techniques for the evaluation of the quality of service on highway and street facilities.” “HCM does not set policies regarding a desirable or appropriate quality of service…” Part I states the purpose of the Highway Capacity Manual (see slide for details).

HCM 2000 Formats Book CD-ROM Five parts, 35 chapters
Audio-visual tutorials CD-ROM presentation The HCM 2000 will come in two formats, a printed book and a CD-ROM. The CD-ROM will contain an electronic copy of the printed book plus a hyperlinked version of the manual with audio-visual aids. No capacity analysis software will be issued with the HCM 2000, as is currently the case. Users will have to obtain capacity analysis software from other sources.

HCM 2000 Table of Contents Part I - Overview Part II - Concepts
Part III - Methodologies Part IV - Corridor and Areawide Analyses Part V - Simulation and Other Models The chapters of the HCM are grouped into 5 parts as shown in the slide. Part III will be the most recognizable because that is where updated versions of the majority of the current HCM chapters will reside. The other 4 parts are entirely new.

Part II. Concepts Describes factors affecting LOS.
Identifies required input. Suggests default values for input. Provides service volume tables Part II chapters describe the factors affecting level of service, identify the input required to compute level of service, and provide suggested default values that can be used to fill in gaps in the available data. These chapters also provide service volume tables that can be used to quickly look up the number of lanes required to provide a target level of service for a given demand volume.

HCM Components This slide illustrates one of the Part II tables identifying required input data and suggesting default values for the computation of signalized intersection level of service.

This slide illustrates one of the Part II tables identifying required input data and suggesting default values for the computation of signalized intersection level of service.

HCM Components and Structure
Chapter 9 is Your Gateway to the HCM Exhibit 9-1 lists facility types and components. The same exhibit gives Part II and Part III chapter references for each facility type. Chapter 9 Provides Guidance on: Use of defaults. Use of or development of service volume tables. Precision and accuracy of results. People wishing to apply the HCM 2000 to a particular problem should start with Chapter 9 in Part I. This chapter provides a road map to the other chapters of the manual. Exhibit 9-1 (shown on following slide) shows the facility types covered in the manual and provides the chapters related to each facility type. Chapter 9 also provides guidance on the use of defaults, the development of custom service volume tables, and the precision and accuracy of results.

Chapter 9 Structure of HCM
This is the left hand side of Exhibit This slide shows the chapters related to the analysis of Urban Streets and Freeways. Chapter 9 Structure of HCM

Chapter 9 Structure of HCM
This right hand side of Exhibit 9-1 shows the chapters related to the analysis of highways, transit, pedestrian, and bicycle facilities. Chapter 9 Structure of HCM

Part III. Methodologies
Provides Methodologies to Compute: Level of Service, Delay, Queues Contents Freeway Facilities (4 chapters) Urban Streets (3 chapters) Highways (2 chapters) Pedestrian & Bikeways (1 chapter) Transit (1 chapter) Part III chapters provide the analytical methodologies to be used to compute level of service, delay, and queues. There are 11 chapters in this part, 4 for freeways,3 for urban streets, 2 for rural highways, 1 each for pedestrians and bikeways, and 1 for transit.

Intersection Control This slide illustrates a diagram provided in Chapter 10 to aid planners in estimating the likely intersection control that would be in place at a future intersection. This figure was prepared prior to the recent FHWA report on roundabouts, and consequently does not reflect the recommendations contained in that report.

Required Data for Signals
This slide illustrates one of the Part II tables identifying required input data and suggesting default values for the computation of signalized intersection level of service.

Level of Service Criteria
This slide illustrates an example service volume table for urban streets. The user enters the table with the demand volume and class of the facility to determine the required number of through lanes. Note that level of service “A” and “B” are impossible to achieve under the default assumptions of signal timing and signal spacing that were used to construct this table. The user would need to construct their own service volume tables for other assumptions of signal timing and spacing.

Transit LOS Criteria

Part IV. Corridor/Areawide
Purpose: How to adapt HCM to planning models Multi-Modal Corridor Analysis Computation of intensity, duration, extent of congestion (for performance measures) Areawide Analysis Capacity analysis for planning models Speed-flow and node delay equations for models A new Part IV has been added to the Highway Capacity Manual that provides guidance on how to extend and adapt the Part III procedures to the analysis of corridors and large areas. The corridor analysis chapter gives guidance on multimodal analyses of corridors. Procedures are provided for computing the maximum intensity, duration, and physical extent of congestion. The area-wide analysis chapter provides guidance to planners wishing to adapt the HCM capacity equations for use in planning models. Special HCM based speed-flow and intersection (node) delay equations are provided for use in planning models

Part V. Simulation Purpose Contents
Guidance on the use of simulation for conditions beyond the bounds of Part III. Contents Chapter 31. Simulation and Other Models Introduction to simulation techniques Part V contains entirely new material on the use of simulation for conditions that fall outside the range of applicability of the traditional capacity analysis procedures described in Part III of the HCM An introduction to simulation techniques is provided.

Using the HCM 2000 Determine Facility Type
See Exhibit 9-1, Chapter 5 Definitions Exhibit 29-2 provides summary. Review Concepts, Inputs, Defaults Review relevant Part II chapter. Conduct Analysis Apply relevant Part III chapter. Interpretation of Results See Chapter 9 discussion on precision. See end of Part III Chapter for sensitivity discussion This slide review the four basic steps involved in applying the HCM 2000 to a capacity and level of service analysis problem. Step 1. Use Exhibit 9-1 and the definitions provided in Chapter 5 to determine the facility type. Exhibit 29-2 summarizes much of this information. Step 2. Review the relevant concepts, inputs, and defaults in the appropriate Part II chapter. Step 3. Conduct the analysis using the procedures described in Part III. Step 4. See the end of each Part III chapter and Chapter 9 for guidance on the interpretation of the results. This concludes Session 1, Overview.

CD ROM Tutorials 4. Delay 3:35 9. Control Delay at Signalized
Intersections 5:50 20. Bicycle Events and Hindrance 3:05 21. Bicycle LOS by Facility Types 4:10 32. Transit Quality of Service 5:05

Highway Capacity Software
No official TRB approved software FHWA sponsored software (2) Windows (Catalina), EZ-HCS written in JAVA Other developers McTrans, Strong Concepts, Dowling, KLD, etc. There never has been, and there is no official Transportation Research Board software for analyzing capacity. The Federal Highway Administration co-sponsoring the private development of two new software products by Catalina Engineering and Iteris for the analysis of capacity. These will be private sector commercial products upon their completion. Other private developers are also developing or updating their software for the HCM 2000. The CD-ROM is supposed to have links that allow users to identity the analysis software that they wish to call from the electronic version of the manual.

Highway Traffic and Safety Analyses Lecture 10: Traffic Control Basics Purdue University School of Civil Engineering West Lafayette

Lecture Outline What control, why, where,
and when use to improve traffic Signs Signals Reading Assignment Example outreach Crosswalks, speed limits, stop signs This seminar has two objectives: 1. To highlight the content and major changes of the Year 2000 edition of the Highway Capacity Manual, and 2. At the end of the seminar attendees will know: Where to find material in the HCM, How to apply the HCM to traffic operations problems, The major changes in methodology between the 1994, 1997, and 2000 HCM

How Make Control Effective
A traffic control device should: Fulfill a need, Command attention, Convey a clear, simple meaning, Command respect from road users, and Give adequate time for a proper response.

Location of Signs

Use of Warning Signs

Where Use Two-Way Stop Signs
A. Intersection of a less important road with a main road where application of the normal right-of-way rule would not be expected to provide reasonably safe operation. B. Street entering a through highway or street. C. Unsignalized intersection on a signalized arterial. D. High speeds, restricted view, or crash records indicate a need for control by the STOP sign.

Which Road Should Have Stop Signs?
The street carrying the lowest volume of traffic If volumes are similar, then The direction that conflicts the most with established pedestrian crossing activity The direction that has obscured vision, dips, or bumps on the approaches The direction that has the longest distance of uninterrupted flow approaching the intersection The direction that has the best sight distance to conflicting traffic measured from the stopped vehicle

Where Use All-Way Stop Signs
A. As an interim measure before installation of the traffic control signal. B. Five or more right- and left-turn collisions as well as right-angle collisions reported in a 12-month period.

C. Minimum volumes: 1. The vehicular volume entering the intersection from the major street approaches (total of both approaches) averages at least 300 vehicles per hour for any 8 hours of an average day, and 2. The combined vehicular, pedestrian, and bicycle volume entering the intersection from the minor street approaches (total of both approaches) averages at least 200 units per hour for the same 8 hours, with an average delay to minor-street vehicular traffic of at least 30 seconds per vehicle during the highest hour, but 3. If the 85th-percentile approach speed of the major-street traffic exceeds 65 km/h (40 mph), the minimum vehicular volume warrants are 70 percent of the above values.

Supplementary considerations A. The need to control left-turn conflicts. B. The need to control vehicle/pedestrian conflicts near locations that generate high pedestrian volumes. C. Locations where a road user, after stopping, cannot see conflicting traffic and is not able to safely negotiate the intersection unless conflicting cross traffic is also required to stop (insufficient sight distances from stopped vehicles). D. An intersection of two residential neighborhood collector (through) streets of similar design and operating characteristics where multi-way stop control would improve traffic operational characteristics of the intersection.

Where Use Yield Signs A. When the ability to see all potentially conflicting traffic is sufficient to allow a road user traveling at the posted speed, the 85th-percentile speed, or the statutory speed to pass through the intersection or to stop in a safe manner. B. If controlling a merge-type movement on the entering roadway where acceleration geometry and/or sight distance is not adequate for merging traffic operation. C. At the second crossroad of a divided highway, where the median width is 9 m (30 ft) or greater. A STOP sign may be installed at the entrance to the first roadway of a divided highway and a YIELD sign may be installed at the entrance to the second roadway. D. At an intersection where a special problem exists and where engineering judgment indicates the problem to be susceptible to correction by the use of the YIELD sign.

Where Use Speed Limit After an engineering study has been made in accordance with established traffic engineering practices, the Speed Limit sign shall display the limit established by law, ordinance, regulation, or as adopted by the authorized agency. The speed limits shown shall be in multiples of 10 km/h (5 mph).

Other Considerations for Speed Limits
A. Road characteristics, shoulder condition, grade, alignment, and sight distance. B. The running speed. C. Roadside development and environment. D. Parking practices and pedestrian activity. E. Reported crash experience for at least a 12-month period.

Where Use Overhead Signs?
A. Traffic volume at or near capacity B. Complex interchange design C. Three or more lanes in each direction D. Restricted sight distance E. Closely-spaced interchanges F. Multi-lane exits G. Large percentage of trucks H. Street lighting background I. High-speed traffic J. Consistency of sign message location through a series of interchanges K. Insufficient space for ground-mounted signs L. Junction of two freeways M. Left exit ramps

SIGNALS

Advantages of Traffic Signals
A. They provide for the orderly movement of traffic. B. They can increase the capacity of the intersection. C. They reduce the frequency and severity of certain types of crashes, especially right-angle collisions. D. They are coordinated to provide for continuous or nearly continuous movement of traffic. E. They are used to interrupt heavy traffic at intervals to permit other traffic, vehicular or pedestrian, to cross.

Disadvantages of Unjustified or Poorly Designed Traffic Signals
A. Excessive delay. B. Excessive disobedience of the signal indications. C. Increased use of less adequate routes as road users attempt to avoid the traffic control signals. D. Significant increases in the frequency of collisions (especially rear-end collisions).

Alternatives to Traffic Signals
A. Installing signs along the major street to warn road users approaching the intersection. B. Relocating the stop line(s) and making other changes to improve the sight distance at the intersection. C. Installing measures designed to reduce speeds on the approaches. D. Installing a flashing beacon at the intersection to supplement STOP sign control. E. Installing flashing beacons on warning signs in advance of a STOP sign controlled intersection on major- and/or minor-street approaches. F. Adding one or more lanes on a minor-street approach to reduce the number of vehicles per lane on the approach.

Alternatives to Traffic Signals
G. Revising the intersection geometry to channelize vehicular movements and reduce the time required for a vehicle to complete a movement, which could also assist pedestrians. H. Installing roadway lighting if a disproportionate number of crashes occur at night. I. Restricting one or more turning movements, perhaps on a time-of-day basis, if alternate routes are available. J. If the warrant is satisfied, installing multi-way STOP sign control. K. Installing a roundabout.

Justifying Traffic Signals
An engineering study of traffic conditions, pedestrian characteristics, and physical characteristics of the location shall be performed to determine whether installation of a traffic control signal is justified at a particular location.

Justifying Traffic Signals MUTCD 4C-3 thru 4C-14
Warrant 1, Eight-Hour Vehicular Volume. Warrant 2, Four-Hour Vehicular Volume. Warrant 3, Peak Hour. Warrant 4, Pedestrian Volume. Warrant 5, School Crossing. Warrant 6, Coordinated Signal System. Warrant 7, Crash Experience. Warrant 8, Roadway Network.

Traffic Study Prior Signals Installation
A. The number of vehicles entering the intersection in each hour from each approach during 12 hours of an average day. It is desirable that the hours selected contain the greatest percentage of the 24-hour traffic volume. B. Vehicular volumes for each traffic movement from each approach, classified by vehicle type (heavy trucks, passenger cars and light trucks, public-transit vehicles, and, in some locations, bicycles), during each 15-minute period of the 2 hours in the morning and 2 hours in the afternoon during which total traffic entering the intersection is greatest. C. Pedestrian volume counts on each crosswalk during the same periods as the vehicular counts in Paragraph B above and during hours of highest pedestrian volume. Where young, elderly, and/or persons with physical or visual disabilities need special consideration, the pedestrians and their crossing times may be classified by general observation.

Traffic Study Prior Signals Installation
D. Information about nearby facilities and activity centers that serve the young, elderly, and/or persons with disabilities, including requests from persons with disabilities for accessible crossing improvements at the location under study. These persons may not be adequately reflected in the pedestrian volume count if the absence of a signal restrains their mobility. E. The posted or statutory speed limit or the 85th-percentile speed on the uncontrolled approaches to the location. F. A condition diagram showing details of the physical layout, including such features as intersection geometry, channelization, grades, sight-distance restrictions, transit stops and routes, parking conditions, pavement markings, roadway lighting, driveways, nearby railroad crossings, distance to nearest traffic control signals, utility poles and fixtures, and adjacent land use. G. A collision diagram showing crash experience by type, location, direction of movement, severity, weather, time of day, date, and day of week for at least 1 year.

Additional Data Recommended
A. Vehicle-hours of stopped time delay determined separately for each approach during the peak hour. B. The number and distribution of acceptable gaps in vehicular traffic on the major street for entrance from the minor street. C. Pedestrian delay time for at least two 30-minute peak pedestrian delay periods of an average weekday or like periods of a Saturday or Sunday. D. Queue length on stop-controlled approaches.

Preemptive Signals Examples:
A. The prompt displaying of green signal indications at signalized locations ahead of fire vehicles, police cars, ambulances, and other official emergency vehicles. B. A special sequence of signal phases and timing to provide additional clearance time for vehicles to clear the tracks prior to the arrival of a train. C. A special sequence of signal phases to display a red indication to prohibit turning movements towards the tracks during the approach or passage of a train or transit vehicle.

Priority Signals Examples:
A. The displaying of early or extended green signal indications at an intersection to assist public transit vehicles in remaining on schedule. B. Special phasing to assist public transit vehicles in entering the travel stream ahead of the platoon of traffic.

Signals Coordination Traffic control signals within 800 m (0.5 mi) of one another along a major route or in a network of intersecting major routes should be coordinated, preferably with interconnected controller units. Signal coordination need not be maintained across boundaries between signal systems that operate on different cycle lengths.

Lecture 11: Traffic Signals Design and Timing Purdue University School of Civil Engineering West Lafayette

Management of Traffic Signals
Major Decisions Need for new signals Signals design and setting Field evaluation Signals improvement Removal of signals

Traffic Signals Studies
Decision Study New signal? Traffic signal warrants study Design and setting Traffic signals design and optimization Field evaluation Delay and queuing studies Signals improvement Individual intersections and corridor studies Remove signals? Alternative control studies

Signals Design and Settings
Signals Needed Non-coordinated Coordinated Full-actuated Semi-actuated Pre-timed Signal phases Signal phases Signal phases Coordinated phase Coordinated phase Change periods Change periods Change periods Control settings Signals timing Detectors type and location

Signals Coordinated or Isolated? Actuated or Pre-timed?
Coordination when 0.5 mile or less between signals Isolated signals when 1 mile or more to the closest signals Cost-effectiveness of coordination should be studied Pre-timed and semi-actuated signals in coordination Full-actuated at isolated intersections

Signal Phases - Left Turns Treatment
Two-lane left turn considered when 300 vehicles per hour or more. Dual Left – most efficient traffic actuated-operation. Various phases and combinations of phases appear only on demand. Lead-Lag (With Overlap)- pre-timed or traffic-actuated. In coordination when the traffic in the opposing directions arrives at different times during a cycle. Opposite/Opposing (Split Phase) – used when the left turns are equal or stronger than the through traffic. Three Phase Operation - the simplest and the least expensive, pre-timed or traffic-actuated. Inefficient when strong traffic disproportion between the opposing approaches.

Signal Phases

Change Periods Y

Change Periods - Yellow

Change Periods – All Red

Pre-timed Signals Timing
Cycle Green split Offsets (coordination)

Settings for Actuated Signals
Minimum green times Maximum green times Gap interval Unit (vehicle) extension Force offs Offsets Cycle length Time-of-day settings

Signal Detectors Vehicle Detectors
1. Inductive loop detectors detect standing vehicles as well as moving ones. The detection area is roughly that enclosed by the loop. 2. Video detectors have similar capabilities as the inductive loop detectors. They require video cameras installed at the intersection. The longitudinal location (setback) of detectors relative to the stop line depends on the speed of traffic and the type of detector operation desired. Bicycle Detectors Bicycle detectors may be required at traffic-actuated signal installations. Type D loop configuration is effective for detecting bicycles and small motorcycles and shall be installed at the bicycle loop detector locations.

Signal Detectors see Northwestern-Stadium

Signal Detectors

Typical Installation

Minimum Green for Pedestrians

Lecture 12: Traffic Signals Design (2) Purdue University School of Civil Engineering West Lafayette

Design Process Phases (Ring Structure) Timing Detectors Coordination
Minimum Green Times Video and Inductive Loop Detectors Signal Cycle Change Periods Phase Splits (Force-off Points) Pulse and Presence Detectors Pedestrian Signals Offsets Maximum Green Times Stop-bar and Advance Detectors Time-of-day (TOD) Plans Vehicle Extension Times Vehicle and Bike Detectors Density Functions

Ring Structure Navigation

Minimum Green Times Absolute minimums = 5 s for left turns
10 s main street through movements 7 s side street through movements Adjustments for unusual traffic volumes are recommended Navigation

Change Periods tr= 1.0 s a = 10 ft/s2 W = intersection width (ft)
L = vehicle length (ft) V = speed (m/h) Navigation

Pedestrian Signals Minimum walk time = 7 s
Pedestrians change period = W/Vp Vp = 4 ft/s in typical situation Walk time + Pedestrian change period must not be longer than the Vehicle maximum green + Vehicle change period Navigation

Maximum Green Times Free Operation
Maximum green time = 1.5 x Green time obtained for X = 0.95 Guidance when optimal splits are not known: Main street maximum green = 75 seconds Side street maximum green = 60 seconds Left-turn maximum green = 50 seconds Maximum green must not be excessively long to avoid discomfort among drivers Navigation

Maximum Green Times Coordination
Maximum green time = 1.3 x Green time obtained from optimization software (Synchro, Transyt, or Passer) Guidance when optimal splits are not known (coordination): Main street maximum green = 50 seconds Side street maximum green = 40 seconds Left-turn maximum green = 35 seconds Maximum green + Change period must not be longer than the time between the corresponding force-off points Navigation

Vehicle Extension Times Stop-bar Detectors
Vehicle extension (s) = 3 – (L+D)/(1.47·V) L = vehicle length (ft) D = detection zone length (ft) V = speed (m/h) Navigation

Vehicle Extension Times Advance Detectors
Vehicle extension (s) = DS/(1.47·V) DS = detection setback (ft) V = speed (m/h) Navigation

Density Functions Minimum Green Extension for Advance Detectors
Maximum initial green = from table below Second/actuation = Maximum initial green/No. of actuations Navigation

Density Functions Variable Gap
Minimum gap = 3 seconds Maximum gap = Min (Vehicle extension, 5 seconds) Time before reduction = 33 % of maximum green Time to reduction = 80 % of maximum green Gap Vehicle extension or 5 s 3 s Time before reduction Green elapsed Time to reduction Navigation

Video and Inductive Loop Detectors
1. Inductive loop detectors detect standing vehicles as well as moving ones. The detection area is roughly that enclosed by the loop. 2. Video detectors have similar capabilities as the inductive loop detectors. They require video cameras installed at the intersection. The longitudinal location (setback) of detectors relative to the stop line depends on the speed of traffic and the type of detector operation desired. Navigation

Pulse and Presence Detectors
Navigation

Stop-bar and Advance Detectors
Navigation

Vehicle and Bike Detectors
Navigation

Signal Cycle Cycle Cycle Cycle Cycle
Obtained from optimization software or calculated for the busiest intersection (X = 0.95) Navigation

Phase Splits (Force-off Points)
Navigation Phase Splits (Force-off Points) Force-off points (F.O.) are obtained from optimization software or from calculations of the average green times for semi-actuated controllers.

Offsets Navigation System zero
Offsets are obtained from optimization software or from a time-space diagram.

Time-of-day Plans Coordination plans (cycle, splits, and offsets) for different time periods Table of plan-to-plan switch times Free mode possible if justified (night?) Navigation

Lecture 13: Traffic Signals Design (3) Purdue University School of Civil Engineering West Lafayette