Travel Time Data and Reliability (Act 1) - Sam Granato

Act I – Incorporating reliability in route choice via link penalties
Act II – Development of formal procedures within TDM software
Act III – New sources of travel time data (enabling reliability
analysis as well as model validation and CMS)

• Not the average time, but the probability you’ll get
there within . . . . .

• Buffer Index (on
freeways only)
estimates “95 th
Percentile” travel
time

“On the clock”
• Horizontal curvature (per
design guides)
• Vertical grades (rural 2-
lane only per HCM)
• Railroad crossings
• Turns at intersections
beyond HCM calcs (A/D
for movements w/out
conflicts, peds, negate
progression)
“Off the clock”
• At external stations
(spread out destinations)
• At state line (tax
differences & related)
• At freeway on-ramps
(BEE book quote)
• Keeping “through trucks”
on designated routes
• NEW – TRAVEL TIME
RELIABILITY

• CV = -0.56 * ln (average delay in seconds) + 2.82; r^2=.73
• Full corridor variability about 90% less than at individual
intersections, so extra time = .1 * 1.645 (95P) * CV * (t-to)
• Also reviewed Phoenix MPO data to extend into more
congested situations (LOS D-F range), CV stops declining
in D-E range

• Little impact on overall validation vs counts or travel times
• Reduces impact of “worst” intersections

Based on research from motorways across the UK
Allows for “automated” setting of impedances at both
link and path level, instead of a “one-off” setting of
penalties based on previous model runs

• Few differences overall due to relative lack of congestion
• Number of Path building iterations has clear impact on
volumes but mixed on validation

• Methods have most impact in delays at the worst
unsignalized approaches

• “Archive” data from vehicle fleets & cell probes
• Extensive road network coverage, could replace or
reduce/redeploy need for “floating car” surveys
• In addition to “real-time” navigation aide, data
history could be used for CMS and/or traffic model
validation
• Has “arrived” at national level (via re-vamping of
TTI’s national Mobility report, major vendor’s
“scorecard” report & use by other DOTs & multistate
coalitions)

• Direction of travel
• Time of day (hour or period)
• Day of week (each day, or weekday vs weekend)
• Season of year (esp. with weather and/or tourism)
• *Vehicle class* (i.e. car vs truck – a considerable
speed difference in some corridors - may not be
feasible yet. Potential for “long haul” vs “mixed
traffic” in short term instead.)

• Sam.granato@dot.state.oh.us
• Or 614-644-6796