Mobility, as a transportation system performance measure, is usually expressed in which units?

Mobility, as a transportation system performance measure, is usually expressed in which units?

• A. Trips per day
• B. Person-miles
• C. Vehicle-miles
• D. Passenger-hours

Answer: (B)

Mobility as a system performance measure is about how far people can move through the transportation network, not just how many trips are made or how far vehicles travel. The natural unit to capture that is the total distance traveled by all people, i.e., person-miles. This combines both how many people are moving and how far they go, giving a clear sense of overall movement through the network. If you used vehicle-miles, you’d be measuring distance traveled by vehicles, which can be misleading when occupancy varies—many people riding in a few vehicles could look the same as many vehicles with few people, even though the actual movement of people differs. Passenger-hours measures travel time, not distance, so it doesn’t reflect how far people are able to move. Trips per day counts engagements but ignores how far those trips carry people. So, person-miles best represents how much movement people experience, making it the standard unit for mobility.

Mobility as a system performance measure is about how far people can move through the transportation network, not just how many trips are made or how far vehicles travel. The natural unit to capture that is the total distance traveled by all people, i.e., person-miles. This combines both how many people are moving and how far they go, giving a clear sense of overall movement through the network.

If you used vehicle-miles, you’d be measuring distance traveled by vehicles, which can be misleading when occupancy varies—many people riding in a few vehicles could look the same as many vehicles with few people, even though the actual movement of people differs. Passenger-hours measures travel time, not distance, so it doesn’t reflect how far people are able to move. Trips per day counts engagements but ignores how far those trips carry people.

So, person-miles best represents how much movement people experience, making it the standard unit for mobility.