NEVADA SPEED MANAGEMENT WORKSHOP Davey L. Warren Office of Safety and Traffic Operations R&D Federal Highway Administration H Reno, NV April 4, 1996

Realistic Speed Limits Why & How n Speed limits and the law n Speed limits, speed and accident risk n Speed limits and driver acceptance n Design speed vs posted speed n Methods for setting speed limits n Recommended approach n Implementation & federal assistance SPEED LIMIT 85 PERCENTILE

Speeding Problem n Rational for government regulation of speed n Speed a factor in 10% of accidents & 30% of fatal crashes n Severity increases with speed n Speed limits widely disobeyed n Conflict between access, safety, and mobility n What is a safe speed & who decides?

Why Do People Speed n Speed set too low n Road design conducive to high speeds n Perceived risk of accident or citation from speeding is low (everyone is doing it) n Fast is consistent with social values n General conflict between mobility & safety

Basic Tenets of Law n Laws protect the public by regulating unreasonable or unsafe actions n Actions of a reasonable person should be legal n Most people drive in a safe and reasonable manner n Law cannot be effectively enforced without the public consent & voluntary compliance

Speed Limit Laws BASIC SPEED RULE -Driver must travel at a speed that is reasonable and proper for conditions and not endanger others or crash. SPEED ZONING -Gives highway agency or localities authority to post limits higher or lower based on an engineering study, and to set them to indicate the maximum reasonable and safe speed.

Speed Laws n Illegal to exceed n Reasonable and safe speed not relevant n Easier to enforce n Not fair unless speed limit set for optimal conditions Exceeding limit is evidence of traveling at unsafe speed n Recognizes no one speed is safe for all conditions n Post for prevailing conditions n Check against traps PRIMA FACIE LIMITABSOLUTE LIMIT

Methods Used To Set Speed Limits n Arbitrary....lack funds & personnel n Political Pressure....based on complaints and reactions to accidents n Traffic engineering....based on traffic and road characteristics...but still somewhat subjective and arbitrarily applied

Current Practice SPEED LIMIT 85 PERCENTILE

Requirements of Speed Limits n Be fair n Be related to risk n Be credible and accepted by drivers n Enforce control over unreasonable behavior SPEED LIMIT 85 PERCENTILE

Speed and Accident Risk n Safest near mean speed of traffic n Roads with highest speeds are safest n Limit should be set at upper end of low risk band ACCIDENTS Freeway Main Rural Two Lane OVERTAKINGS Relative Risk Deviation from mean speed, mi/h

Accident Risk in Built-up Areas Percentile Speed

Speed of traffic best indicator of reasonable and safe speed Relative Risk Deviation from mean speed, mph OVERTAKINGS ACCIDENT INVOLVEMENT SPEED LIMIT 85 PERCENTILE

Driver Acceptance n 30% nationwide n Range from 3-100% n Worse with low limit n Better in west/midwest n Better w/prima facie n Only 1 speed zone in 10 better than 50 percent compliance Group Mean % %Compliance

Most Limits Set Way Below Prevailing Speed n Prevailing speeds 8-12 mph above limit n Trucks 3 mph slower n Speeds vary 4-8 mph over a 24-hr day n No difference between weekday & weekend Operating Speed

Factors Influencing Speeds n Number of access points along road n Commercial development n Severe curvature n Level of accidents n Adverse weather

Minimum Design Speed n All geometric elements must meet or exceed n Only when constrained by terrain or development is minimum used n Maximum safe speed for worst driver under bad road conditions n Reaction time of drunk drivers, stopping with bald tires on slippery road, average comfort level of blind folded passengers in 1930 vintage car

Raising limit has little effect on prevailing speed of traffic

Lowering limit doesn’t slow traffic

Little or no change in behavior Change in 85th Percentile Speed, mi/h -15 & & +15 Change in Posted Speed Limit, mi/h Average Change Maximum Increase Maximum Decrease

Compliance before and after change Percentage of Driver Compliance -15 & & +15 Change in Posted Speed Limit, mi/h BeforeAfter

Accidents Before & After Percent Change in Crashes Lowering Speed LimitRaising Speed Limit Upper Estimate Lower Estimate Best Estimate

n Most speed limits set unreasonably low Make technical violators out of large percent of motorists driving at safe speed n Current speed limits do not reflect accident risk Inconsistent with traffic law system Misallocates enforcement resources n Most motorists drive at a speed road and traffic permits regardless of posted speed Don’t automatically drive 5 mph over limit n Speed limits have lost their informational value Engineering of credible limits which are appropriate and enforceable the key to managing risk What We’ve Learned

Recommended Procedure 85 PERCENTILE SPEED LIMIT n 24hr free flow speed n Round up n 1/2 mile interval n 500ft from jct. & curves n Dry roads, typical traffic n No other adjustments

Design Speed vs Maximum Curve Speed Source: FHWA-RD Design Min. Tolerable Min. Impending Impending Rollover Speed E Lateral Gs Radius Skid (wet) Skid (dry) Car 40 mi/h ’ 63.3 mi/h 87.5 mi/h 98.1 mi/h 70 mi/h ,083’ mi/h mi/h mi/h Car: f(dry) = 0.65

Special Zones n School zone - Base on average speeds when children present Restrict to minutes periods when kids present n Work zones Base on average speed during good conditions Use warning sign for hidden hazards & post advisory speed at average speed of traffic when hazard exits Vary limit based on speeds when work in progress

Residential Areas n Post at 85% rounded to nearest n If lower limit desired, must change the road environment n Road humps, traffic circles, etc. n Confine engineering measures to small area

General Approach n Engineer rational speed limits n Educate and inform public Hazards of traveling too fast or too slow Limits engineered to be safe & reasonable n Strict enforcement and adjudication Eliminate tolerances & inform judiciary n Evaluate Effects on drivers, safety, police, courts SPEED LIMIT 85 PERCENTILE

Key Benefits n Respect for law and enforcement n Effective allocation of resources n Deterrent to excessive speed by clearly separating occasional violator from majority n Reduce conflicts caused by large variations in travel speeds n Improved road safety and better use of roads SPEED LIMIT 85 PERCENTILE

Federal Fund$ Available Engineering Education Enforcement Evaluation

$ n Mileage of roads to be rezoned by class n Frequency and duration of speed studies n Public information and outreach plans n Enforcement and judicial cooperation n Evaluation n Estimated total cost and cost share Next Step-Application to practice

Where to get more information Greg Novak Federal Highway Administration 705 N. Plaza Street, Suite 220 Carson City, NV  fax SPEED LIMIT 85 PERCENTILE