Transit Travel Time

Planned trip time combines average travel time and variation to generate a single number, such as the 50th or 85th percentile travel time, reflecting a typical traveler’s experience of the mobility system. Comparing these numbers across modes for a trip along the street, or for a set of trips around the network, helps evaluate the real time saved by transit street design changes. Pedestrian travel time which is affected by the completeness of the pedestrian network and by signal timing and the distance between crossings, should be added to provide a more accurate view of total travel time.

At the network level, the planned travel time can be used to evaluate the effects of a transit street project on the performance of the system as a whole. When applied to the entire city or region in relation to demographic and employment location data, planners can evaluate the number of jobs, businesses, or other neighborhoods accessible by transit within a target travel time. The equity of the transportation system can be evaluated using this method, by comparing the level of access provided to each neighborhood.

Across modes, delay compared with free-flow movement is important for understanding the potential value of various transit priority treatments, but is less meaningful when considering personal mobility. Use delay and queuing to inform intersection-specific design treatments, such as the size of pedestrian refuge areas or upstream traffic signal management. Changes to vehicle queue length at key intersections may be relevant to the perception of a project’s impacts, and should be understood in the context of overall street operations and impacts on cross streets.

Access to the City

A primary metric for evaluating the effectiveness of a transportation system is the number of destinations—rather than the physical territory or distance—reachable by residents in set amounts of time. Applying this measure to the transit-walking system creates a master effectiveness metric that can be applied to evaluate potential large transit investments or changes in transit network structure.

Measuring vehicle traffic volume (throughput) before and after project implementation can provide information about mode shifts and spatial or temporal diversion, when network-level traffic data is available. As development occurs along a transit corridor, quantifying the total number of people using the street demonstrates the total value of the places along the street, and is a relevant measure for understanding the new destinations available to motorists in a given travel time.

Consider network-level evaluation for transit street elements that are expected to lengthen a street’s travel time for private vehicles, but may add significant transit capacity and eventually reduce vehicle trip demand.  As mode shift occurs on the corridor, traffic volumes may decrease or remain constant.

At the city or region level, vehicle miles traveled and transit passenger miles traveled are key performance measures whose direction indicates whether a city is becoming more or less dependent on private vehicle travel. Commute mode split is an important and commonly used measure, and should be supplemented by measures of mode split for other trip types.

Curbside Management

Loading, parking, and curbside management are important regulatory facets of transit street project planning and evaluation. Transit street design treatments sometimes increase or decrease parking supply. Changes in on-street parking supply can be quantified by calculating the percentage change to the number of residential or commercial (metered) spaces available within a short walk of the transit corridor.

In cities, goods movement efficiencies are relevant for both travel time and loading. The number of illegally parked or double-parked trucks, or the time spent by a truck looking for a loading space, can be used to measure the effectiveness of curbside management for goods movement along a transit street.

Since severe crashes are relatively rare events, it may be necessary to evaluate the safety of a street before statistically significant or reliable data is available on KSI crashes.

For faster analysis, changes in the top or 99th percentile vehicle speeds, or the percentage of vehicles operating above the target speed, may be used to understand the effectiveness of safety measures and changes in the risk of serious injury to transit occupants and pedestrians, soon after a project is implemented.

Conflict counts, which measure the number of evasive actions taken to avoid an imminent crash at a specific location, can be used in conjunction with other engineering assessment tools to understand the safety performance of a particular street redesign.

At the city or regional level, the number of transportation injuries, severe injuries, and deaths; and injury rates per capita are primary safety performance metrics. The safety performance of transit vehicles and systems can be measured in injuries or crashes per revenue mile or injuries per passenger mile traveled. However, since limiting or reducing the total miles of vehicle travel in a region is a major motivation for transit investments, evaluations of multi-modal safety should avoid denominating by distance traveled.

Safety can be evaluated at an operational level more quickly than crash data analysis permits, allowing potentially life-saving changes. 95th percentile vehicle travel speed and the percent of vehicles exceeding the speed limit or exceeding the street’s target speed can be used to evaluate the effectiveness or consistency of traffic operational measures on the street. Measures of conflicts per day between motor vehicles and pedestrians or bicyclists can be used to quickly assess whether specific safety issues have been addressed by a design treatment.

The quality of public space is a leading indicator for both transit and business potential. Public space canvassing, which counts the number of people engaged in stationary activity in a place, is a measure of public space quality and availability. For projects with a public space component, this measure provides hard data to support quality-of-life conclusions. Supplement these observational counts with survey data on public space quality and project satisfaction for a more comprehensive understanding of the experiential quality of a public space.

Sidewalk comfort and safety can be quantified using measures relevant to human comfort, including the availability of shade, adequate street lighting, and active ground floor uses. Develop measures specific to the project, climate, and social life of the street.

Physical activity related to added or improved transit can be measured in daily time spent being active or distance walked or biked. Increases in physical activity may be correlated with changes to the built environment that increase transit ridership, such as increased density or walkability.

Increasing transit mode share on a street can dramatically improve the street’s air quality, with benefits for public health and sustainability. Air quality can be measured and compared across modes as emissions per occupant mile, with greenhouse emissions and particulate emissions singled out as areas of special concern.

Surface permeability ratio, pavement reflectivity, and surface air temperature are affected by the amount of paved area, and the type and color of material used.