Travel Speed Study of Urban Streets Using GPS &GIS Tom E. Sellsted City of Yakima, Washington Information Systems and Traffic Engineering Divisions

Overview  Why conduct a Travel Speed Study and basic components.  GPS/GIS as a tool for real time data collection  Using ArcView 3.2 and Crystal Reports to Analyze data

Transportation Planning  Washington State Growth Management Act requires cities to maintain a Transportation Plan, including level of service, capacity needs and future planned projects.  Plans must identify deficiencies and planned projects

Travel Speed Study  Average Travel Speed is the basic service measure of urban streets which includes the running time on the street segment and control delay of through movement at signalized intersections. (Highway Capacity Manual, 2000)  Planning Level application, not for signal timing or progression studies.

Highway Capacity Manual  Published by the Transportation Research Board, National Academy of Sciences and Engineering. Last update 2000  Primary reference used by Traffic Engineers which establishes procedures and standards.  GIS/GPS not widely used yet in Traffic Engineering standards

Key Components Average Travel Speed was determined using the following formula: S A = 3600 L / T R + D S A = Average Travel Speed L = segment length (miles) T R = total Running Time for each segment (seconds) D = Average stopped delay during PM peak hour traffic (seconds)

Actual driving time during “free- flow” conditions

Stopped Delay Stopped Delay is the time the vehicle is either stopped or moving at a very reduced rate of speed either at an intersection or along the travel route. For this study the measurement of “delay” was if the vehicle was moving less than 12 miles per hour.

Travel Speed is dependent upon the length of delay experienced during PM peak hour traffic

Methodology  Starting and ending times were recorded with a synchronized stop watch for data retrieval.  Study Route designed without any overlapping segments to avoid duplicate points.  Avoid left turns at signalized intersections, if possible to avoid left turn delay.  Only one Study Route driven each day during PM Peak Hour, to avoid confusion in points and capture peak hour conditions.

Driving Routes

Segmenting the Urban Streets  Streets were ordered with respect to their functional classification and design characteristics. Study included 85 miles of streets  HCM specifies LOS standards.  Attribute Table developed for each of the 80 street segments.

Urban Street LOS Highway Capacity Manual, Exhibit 15-2

Optimized travel time was calculated for each street segment: FFe = (60 * (L/5280)) / speed limit Where: FFE = Estimated Free=flow travel time in minutes L= Length in miles of each street segment Speed Limit = posted speed limit Estimated Free-Flow Time

Data Collection Driving during PM peak hour conditions required the driver to emulate the stream of through traffic, matching the speed of another vehicle; avoiding aggressive or unusual behavior; Each segment driven a total of 6 times, evenly split by direction. Peak hour study conducted Monday through Thursday.

Automated GPS Collection  GPS is an efficient and accurate tool for collecting vehicle position and speed  One driver instead of a driver and a technician  No stop watches or clipboards  Safety

GPS System Characteristics  GPS data was collected using a Sierra Wireless MP200 CDPD modem with GPS option.  City of Yakima Public Safety Departments currently using system for various applications.  GPS data transmitted back to central Automated Vehicle Location (AVL) server.

Importing GPS Data into GIS  Script was written in Avenue to import position reports from the field and create a table of position and time information for analysis.  Data imported in latitude and longitude, then projected into state-plane coordinate system  Table includes fields for unit, position ID, heading, GPS speed, date, time and delay.

2-Second Interval  Vehicle positions were gathered at 2-second intervals and 12-meter distance. The position will not be transmitted unless the vehicle has moved 12 meters or more, AND 2 seconds has elapsed.  Time interval is easily configured on the GPS unit by sending a Trimble ASCII Interface Protocol (TAIP) message, such as >DPV <

Data Gaps Significant distance between data points can be caused by several factors: Buildings, trees or other objects block clear satellite view of the GPS antenna Topography may difficult in some locations Period of time when dilution of precision (DOP) is not suitable

Tree Canopy on 3 rd Ave

Joining GPS Shape files to Routes  Route Number, Date and Run Time are imported for each segment and joined to the Route Shapefile using a dialog request box.  Other GPS attributes such as heading, speed, and delay are joined to the shapefile as well.

GPS dialog box

Hand Editing of Points  Reduction of data points was automated by the importing of data generated during a specified time period and within 150 feet of the route end points.  Visual inspection and editing of the points at each end point of the route segment eliminated extraneous points or those from an adjoining route.

editing

Computation of Delay  AVENUE Code was used to calculate delay, duration and distance between points  Time values from the database were numbers which needed to be calculated as seconds.  Point values in seconds were stored and compared to previous point values

AVENUE Code

Crystal Reports for Analyzing Data  Free-flow data and Speed Study GPS data points were analyzed using Crystal Reports  Great reporting tool because of the ability to add multiple break points in the data.  Ability to sort data by driving routes, street segment, direction, date and time

Crystal

map

Peak Hour Traffic pic Summary: GPS is a very efficient tool in collecting traffic data. Dynamic features of GPS data capture position, time and speed. Analysis of this robust data is possible using GIS tools. Presentation of data is enhanced through GIS.

Travel Speed Study of Urban Streets Using GPS &GIS Tom E. Sellsted City of Yakima, Washington Information Systems and Traffic Engineering Divisions