SHRP 2 Project L07:

1. Evaluation of the Costs and Effectiveness of Highway Design Features to Improve Travel Time Reliability SHRP 2 Project L07: 

2. Objectives for L07 • Identify All Roadway Design Features Used to Improve Travel Time Reliability and Reduce Delays From Non-Recurrent Congestion • Assess Their Costs and Effectiveness at Improving Travel Time and Safety • Provide Usage Recommendations Via Design Guides

3. Objectives for L07 Identify All Roadway Design Features Used to Improve Travel Time Reliability and Reduce Delays From Non-Recurrent Congestion • Traffic Incidents • Weather • Demand Fluctuations • Work Zones • Special Events • Traffic Control Devices

4. Objectives for L07 Identify All Roadway Design Features Used to Improve Travel Time Reliability and Reduce Delays From Non-Recurrent Congestion • “The level of consistency in travel conditions over time, measured by describing the distribution of travel times that occur over a substantial period of time.”

5. Measuring Reliability • Travel Time Index (TTI): The ratio of the actual time spent traversing a given distance to the free-flow travel time for that same distance. • Ex: 60 mph free-flow over 2 miles • Takes driver 2.5 min, normally takes 2.0 min • TTI = 2.5/2.0 = 1.25

6. Solution: The Cumulative TTI Curve

7. Solution: The Cumulative TTI Curve • Lateness Index Total Delay = LI × V × TTFF LI = Lateness Index V = Volume TTFF = Free Flow Travel Time

8. Solution: The Cumulative TTI Curve

9. Sources of Data • Crash data from HSIS • Total crashes, Fatal/Injury, Property Damage Only • Weather Data from NCDC • 10 yrs of hourly precip data across US • Focus Groups with Highway Agencies • What design treatments are you using?

10. Objectives for L07 • Identify All Roadway Design Features Used to Improve Travel Time Reliability and Reduce Delays From Non-Recurrent Congestion

11. Crash data from HSIS • Total crashes, Fatal/Injury, Property Damage Only • Weather Data from NCDC • 10-years of hourly precip data across US

12. Design Treatments • Emphasis on Design Treatments that Targeted Nonrecurring Congestion • Adding a shoulder for crash investigation/ vehicle pullout vs. widening lanes

13. Objectives for L07 • Identify All Roadway Design Features Used to Improve Travel Time Reliability and Reduce Delays From Non-Recurrent Congestion • Assess Their Costs and Effectiveness at Improving Travel Time and Safety • Provide Usage Recommendations Via Design Guides

14. Factors in Forecasting Reliability • (1) A general measure of highway congestion (ratio of demand to capacity) • (2) A measure of temporal-spatial impacts of incidents and work zones (lane-hours lost) • (3) A measure of precipitation amount over a specified period (rain and snow)

15. About The Research • Three separate analyses conducted • Analyze improvement in TTI • Analyze improvement in safety • Analyze costs/benefits based on these improvements

16. Analyzing Treatment Effects • Direct calculation of performance measures from field data • Deterministic analysis techniques [using HCM] • Microscopic traffic simulation • Qualitative methods, where necessary

17. Deriving TTI Curves • Drew on formula developed in L03 • TTIn% = e(j*LHL + k*dc + l*R) • TTIn% = nth-percentile TTI value • LHL = lane-hours lost • dccrit= critical demand-capacity ratio • R0.05” = hours of rainfall exceeding 0.05 in • jn, kn, ln= coefficients for nth percentile

18. Estimating Demand and Capacity • Volume, speed data gathered in 5-min intervals where mean speed drops into congested range • Traffic queue forms, begins to dissipate midway through congested period • Total demand estimated (Method discussed in L03) • Alternative: d= v30 + q

19. Estimating Demand and Capacity • Capacity (c) = Free flow speed * lanes • Capacity can be varied through strategies such as reversible lanes • Dccrit = d/c

20. Estimating ILHL • ILHL: The effective number of lanes blocked due to all incidents occurring during a timeslice, multiplied by the average blockage time for each incident type.

21. Estimating ILHL • Number of incidents of each type calculated using data collected for frequency of incident types as a function of traffic density • # Lanes Blocked = Total Lanes*(1-Rcap,i) • R = capacity reduction ratio for incident type i • Values of Ri found in HCM • Incident Time:

22. Deriving TTI Curves • Drew on formula developed in L03 • TTIn% = e(j*LHL + k*dc + l*R) • TTIn% = nth-percentile TTI value • LHL = lane-hours lost • dccrit= critical demand-capacity ratio • R0.05” = hours of rainfall exceeding 0.05 in • jn, kn, ln= coefficients for nth percentile

23. Objectives for L07 • Identify All Roadway Design Features Used to Improve Travel Time Reliability and Reduce Delays From Non-Recurrent Congestion • Assess Their Costs and Effectiveness at Improving Travel Time and Safety • Provide Usage Recommendations Via Design Guides

24. What Does the Tool Do? • Analyzes homogenous freeway segment between interchanges • Calculates base reliability from inputs • User inputs basic data about treatment • Generally just% incidents that will use it, approx duration of incidents with treatments • Estimates new TTI curve and runs cost/benefit analysis

25. Demo Tool!

26. Questions?