Tidbit Tuesday
Tuesday, January 07, 2020 at 6:40:54 PM

Let’s Talk About Demand

Demand has been a hot topic lately, so we’d like to answer some of the questions we’re getting: how to measure it, how to calculate it and how to put it in software correctly. To make it more palatable, we’re going to do a multi-part series to answer those questions.

To start things off, let’s talk about what demand is. The number of vehicles who want to go through an intersection during a certain time is demand. To measure demand, you need to know how many and when those vehicles want to go through the intersection. It’s not feasible to have sensors everywhere, so we use tubes, turning movement counts (TMCs), queues, and formulas.

To effectively capture demand, TMCs are taken during the peak period (not peak hour). If you’ve identified your peak period correctly, a bell curve of volumes should appear, peaking in the middle and starting/ending in a flat line. That’s because everyone who wanted to get through the intersection during the peak period was able to do so.

Capturing each approach in this fashion gives us the distribution of volumes that allows us to analyze and interpret the true demands of that intersection. This results in better geometric designs, more accurate signal timings and a defendable analysis, even in highly congested areas.

Thanks for reading and stay tuned for our next installment on demand. If you'd like to contact us with any comments, questions or tidbits of your own, please email TrafficEngineering@la.gov. Thanks for reading!