Transport

Road Metrics

From Latency to Bandwith

Simple Road Segments

Consider a hypothetical segment of road. Suppose this segment is short enough that all the vehicles on it move at the same speed.

Suppose we wanted to “measure” the “state” of this road, using various metrics. What metrics might we care about?

Distance and Speed

The most “well-known” metric about roads is probably distance. Or the length of the road segment. The other “well-known” metric is “speed”. Or the distance travelled in a unit time.

For example, if some road segment is 100m, and it takes 10s for a vehicle to move from one end to the other, the “speed” on this segment is “10 meters per second” or 10m/s. Or in more familiar units, 36 km/h.

Latency

We also care about how much time it takes to get from A to B. For the example road segment, this time or “latency” is 10s.

Bandwidth and Density

The “bandwidth” of a road is the number of people that can travel through in a unit time. Bandwidth depends on both speed, and how densely people can pack into the vehicle travelling on that road.

For example, a large, 10m-long bus carrying 50 people, carries 5 people/m. A 5m-long sedan, carrying 5 people, carries only 1 person/m.