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DRAFT |
| Type of Performance Measure | Performance Measure | Definition/Description | Required Metrics | Why It Is Important to the MPO Region | How It Will be Displayed | Previously Used by Boston Region MPO? | Performance Measure Recommended by MPO Staff? |
| Duration1 | Congested
Time |
The average number
of minutes that drivers experience congested conditions, at speeds below
35 mph, during the peak period. Congested Time (Minutes) = (# of Minutes with Speeds below 35 mph / Total Number of Minutes in Sample) * (Number of Minutes in Peak Period) |
● Speed ● Congested speed threshold (35 mph) |
● Can track the
average number of minutes that each Traffic Messaging Channel (TMC)2
or corridor segment is experiencing congestion ● Can be a key factor for a corridor analysis in the LRTP needs assessment. |
GIS mapping for the region by TMC | No | Yes |
| Duration | Annual
Traveler-Hours of Delay and Annual Vehicle-Hours of Delay3 |
Measures
the total amount of delay that a TMC will experience on an annual basis.
It is calculated by factoring the amount of time it takes to traverse a
given TMC during the peak period minus the amount of time it would take
to traverse that TMC in free-flow conditions, multiplied by vehicle
volume per period, multiplied by vehicle occupancy, multiplied by the
number of weekdays per year, divided by 60 minutes. For this measure it
is assumed that there are 250 weekdays per year. Annual Traveler-Hours of Delay = (Average Travel Time - Free-Flow Travel Time) * Vehicle Volume per Period * Vehicle Occupancy * 250 weekdays Annual Vehicle-Hours of Delay = (Average Travel Time - Free-Flow Travel Time) * Vehicle Volume per period * 250 weekdays |
●
Average travel time ● Free-flow travel time ● Vehicle volumes ● Vehicle occupancy data |
●
Can be a key factor for a regional or subregional analysis for the LRTP
needs assessment ● Displays the extent of delay experienced throughout the region on a per-traveler basis |
GIS mapping for the region by corridor; Histogram bar; or table | No | No |
| Extent4 | Lane-Miles of
Congestion |
Measures the extent of congestion on a facility based on geographic span. Each TMC is categorized as congested or uncongested depending on the Speed Index value (under Intensity, below). This measure is stated as a percentage of total lane-miles. | ● Lane-miles ● Number of lanes for each roadway segment ● Speed Index thresholds |
● Shows the regional
congestion level by facility ● May be suitable for a regional or subregional analysis in the LRTP |
Stacked bar graph or table | No | Yes |
| Extent | Percent of Congested Roadway Miles | This measures the percentage of freeway miles that experiences an average speed of less than 35 mph (congestion threshold). | ● Segment length ● Average Speed |
● Can give a
regional or subregional snapshot of what facilities are congested ● Can be used to compare subregions for the LRTP |
Stacked bar graph or table | No | No |
| Extent | Freeway Congestion
Scan |
Visually displays
average speeds for a corridor for multiple times of the day, at multiple
locations. |
● Average speed | ● Enables users to
visually see where and at what time a roadway is congested |
Line chart and/or table | No | Yes |
| Extent | Congested
Travel3 |
Captures the extent
of congestion by displaying the amount of vehicle-miles traveled under
congested conditions (less than 35 mph). Congested Travel = Congested Segment Length * Vehicle Volumes |
● Segment length ● Vehicle volume ● Average speed ● Congestion threshold |
● Displays the extent of congestion, as it affects traveling vehicles, on a corridor level | Histogram bar graph or table | No | No |
| Extent | Vehicle-Hours of
Travel3 |
Total amount of time
that every vehicle spends traveling through a roadway segment, corridor
or region within a specified period of time. Vehicle-Hours of Travel = Travel Time * Vehicle Volumes |
● Traffic volume
● Travel time |
● Displays the extent of congestion | Histogram bar graph or table | Yes, through the regional travel demand model | No |
| Extent | Vehicle-Miles
of Travel3 |
Total
number of miles that every vehicle travels through a roadway segment,
corridor or region within a specified period of time. Vehicle-Miles of Travel = Segment Length * Vehicle Volumes |
●
Vehicle volumes ● TMC length ● Average speed |
● Displays the extent of congestion on a corridor level | Histogram bar graph or table | Yes, through the regional travel demand model | No |
| Extent | Delay
per Traveler or Vehicle3 |
Measures
the amount of delay that a vehicle or a traveler would experience each
time it traverses the TMC at a given time. This measure can be used to
communicate to a nontechnical audience. Vehicle occupancy data would be
required for Delay per Traveler, and it would be difficult to obtain for
all locations. Delay per Traveler (Minutes) = (Average Travel Time - Free-Flow Travel Time) * Vehicle Volume * Vehicle Occupancy Delay Per Vehicle (Minutes) = (Average Travel Time - Free-Flow Travel Time) * Vehicle Volume |
●
Vehicle volumes ● Free-flow travel time ● Average travel time ● Vehicle occupancy data (for Delay per Traveler only) |
● Communicates to the public the impact of delay caused by traffic congestion on a user level | Histogram bar graph or table | No | No |
| Intensity5 | Average Travel
Speed |
Average Travel Speed is associated with specific roadway TMCs and iscalculated using travel times and segment lengths. The average observed travel speed is a good indicator of a deficiency in mobility in the roadway network and is used for determining solutions to mobility problems. | ● Average travel speed | ● Indicates where
congestion is located by corridor segment ● It is an integral entity for calculating other performance measures. ●Measure can be converted into travel time. |
GIS mapping for the region by corridor | Yes | Yes |
| Intensity | Average-to-Posted-Speed Ratio (Speed Index) |
Equal to the average
speed divided by the posted speed limit of a TMC. TMCs with an
Average-to-Posted-Speed Ratio of 0.70 or less are considered to be congested. This
measure indicates congestion more accurately than travel speeds alone
because low travel speeds may be a result of low speed limits on certain
facilities. Speed Index = Average Travel Speed / Posted Speed |
● Posted speed
(speed limit) ● Average travel speed |
● Shows speeds in
relation to the posted speed limit |
GIS mapping for the region by TMC | Yes | Yes |
| Intensity | Bottleneck
Factor |
This factor
combines both the duration of time
a TMC is congested and the intensity of congestion. It
can be used to rank problem areas of the freeway network. Bottleneck Factor = Minutes of Congestion per Peak-Period Hour / Congested Speed |
●
Congested Time ● Average speed, when congested |
●
May be used to further evaluate sections of the roadway network for
bottlenecks ● Can be used to rank bottlenecks on a regional or subregional basis in the LRTP needs assessments |
GIS mapping for the region by TMC | No | Yes |
| Intensity | Delay
per Mile |
Delay
shows the extra time needed to traverse a TMC or corridor. Delay can be
converted into delay-per-mile by factoring in the length of the roadway
segment. ((Average Travel Time (Minutes) - Free-Flow Travel Time (Minutes)) / Segment Length |
●
Free-flow travel time ● Average travel time ● TMC length |
●
Displays the impact of delay on a corridor ● Can be a key factor for corridor analysis in the LRTP needs assessment |
GIS mapping for the region by corridor | No | Yes |
| Intensity | Calculation
of Congestion Score |
Calculated
by integrating the results of several performance measures by applying
weight factors. To calculate congestion scores, performance measure
values are placed in several classes. Each class is assigned a point
value representing the intensity of congestion associated with that
performance measure value. The point values are then totaled, giving the
segment a final congestion score. A segment's final congestion score is
an indicator of the intensity of congestion for that segment, with the
level of intensity increasing with the score value. |
●Various performance measures of extent, duration, reliability, and intensity. The selection of performance measures for analyses often varies. | ●
Can be used in the LRTP ● Can be a tool for determining congested locations for the Congestion Management Process ● Possibly useful for evaluating TIP projects |
GIS mapping for the region by TMC | No | No |
| Reliability6 | Travel-Time Index
(TTI) |
Dimensionless
quantity that compares travel conditions during the peak period to
travel conditions during free-flow conditions, defined as the ratio of
peak-period time to free-flow time. For example, a TTI of 1.20 indicates
that a trip that takes 20 minutes in the off-peak period will take 24
minutes in the peak period, or 20 percent longer. Travel-Time Index = Average Travel Time / Free-Flow Travel Time |
● Average travel
time ● Free-flow travel time |
● Can indicate how
severe peak-period congestion is on a facility, compared to off-peak
travel ● Can influence future decisions that may be proposed to alleviate a congested corridor ● Good tool for gauging reliability through the LRTP and CMP |
GIS mapping for the region by TMC | No | Yes |
| Reliability | Planning-Time
Index |
Defined
as the ratio of the total time needed to ensure on-time arrival 95
percent of the time to free-flow travel time. It differs from the
Buffer-Time Index (below) in that it includes typical delay as well as
unexpected delay. Thus, the Planning-Time Index compares near-worst-case
travel time to free-flow travel time. For example, a value of 1.4 means
that, to arrive on time 95 percent of the time, a traveler should budget
an additional 8 minutes for a trip that takes 20 minutes during
free-flow conditions. Planning-Time Index = 95 Percentile Travel Time / Free-Flow Travel Time |
●
95th percentile travel time ● Free-flow travel time |
●
Can be used in the needs assessment as a corridor measure. Parallel
routes can be compared with one another, which can indicate what route
is ideal for commuters and incident responders. ● Can tell daily commuters how much extra time to budget to ensure on-time arrival |
GIS mapping for the region by corridor | No | Yes |
| Reliability | Buffer-Time
Index |
Measures trip
reliability that expresses the amount of extra buffer time needed to
arrive on time for 95 percent of the trips taken. The difference between
the Buffer-Time Index and Planning-Time Index is that the Buffer-Time
Index factors in the average travel time instead of free-flow travel
time. Buffer-Time Index = (95 Percentile Travel Time - Average Travel Time) / Average Travel Time |
● 95th percentile
travel time ● Average travel time |
● Can tell a commuter what to expect if a certain amount of time is allowed for a commute (e.g., late for work on one day out of the typical 20-workday month.) | GIS mapping for the region by corridor | No | No |
| 1 Duration performance measures indicate the amount of time congestion affects a region, corridor, or roadway segment. | |||||||
| 2 The TMC location code is a common industry convention, developed and maintained by the leading electronic map database vendors to uniquely define road segments. | |||||||
| For freeways, a TMC is defined as the segment between two interchanges. | |||||||
| 3 MPO staff may not have the required metrics to calculate this performance measure. | |||||||
| 4 Extent performance measures estimate the number of people or vehicles affected by congestion, and the geographic distribution of congestion. | |||||||
| 5 Intensity performance measures indicate the severity of congestion. It is typically used to differentiate between levels of congestion on transportation corridors. | |||||||
| 6 Reliability performance measures show the impact of nonrecurring as well as recurring congestion in the travel network. | |||||||