Travel Time vs Delay Time

Making sense to the motorist

Communicating the effect of a queue on a drivers experience can be difficult. You want the message to the motorists to be easy to understand, and contain valuable information. Getting the valuable information to them is the easy part, our software calculates the real-time travel time based on what sensor data is available and outputs a number. Its the wording of the message that can get tricky. Heres some things to consider.

Difference between travel time and delay time
  • Travel time is how long it will take from seeing the message to arriving at a destination.

This is the more common strategy of informing motorists of queue time. It gives them a firm number to compare against.

  • Delay time is how much longer will it take than usual to get to a destination.
Removing ambiguity:

The thing most often left out of travel time messaging is a specific destination. I've seen it countless times, where the message will say "Travel time to Downtown 15 minutes". Well where does Downtown actually begin? It could be 15 minutes to anywhere near downtown. This kind of ambiguity might have passed in years prior, but with the explosion of smart phones, and everyone using Waze and other GPS routing software, people expect a better experience. We'll go into detail on each of the ways to accomplish this, but heres a quick list to get us started:

  • XX Miles XX Mins
  • Travel time to specific roadway
  • Travel time to end of work zone
  • Dual travel times / Delay Time
XX Miles XX Mins

Utilized by a few DOTs around the country, such as MassDOT and IDOT, this is a good way to include an accurate destination to the travel time. Typical messages pushed to a VMS might look like "Location A to Location B / XX Miles XX Mins". MassDOT even includes the current time in their messages. The advantage here is that you can notify drivers of how long it will take to travel from a destination downstream to another destination down stream. This is perfect for message signs far out, on the edge of your project, that don't have sensors nearby.

Travel time to Specific Roadway

"Time to Main St / XX Mins" this message style is best used on the lead up to your work zone where you have decent sensor density. If you're considering using specific road names (Main St, France Ave, etc), you should do it only on commuter roads. Exit numbers might be a better destination choice for high truck traffic roadways.

Travel time to end of work zone

"XX Mins to end of WZ" works well for longer work zones (greater than 3 miles). Message signs can be placed near "Road Work Ends X Miles" static signs to reinforce and reassure, that this will be over soon. This type of message necessitates sensors within the workzone. If you are already concerned about an accident occurring within your workzone (due to lane shifts, uneven pavement, etc), this might be a good way to add a travel time component to a queue warning / prepare to stop system.

Dual Travel Time / Delay Time signs

These are wonderful, but rare. They are really only viable prior to forks in the road where the two options lead to the same destination (eventually). If the destination is reachable within 3x the travel time on either route, this is a good option to present. If these conditions are met, this is one of the best and most beloved systems out there (anecdotal evidence only, but I've heard rave reviews from the public when I've deployed these systems). They are just so clear and allow the motorist to make their own choice.

Sensor Considerations

When considering what sensors you want for your project, remember that if low speeds are expected (<20mph) dopplers are the best bet. Not many systems typically have travel times weighted by volume, at least for their real-time information, so volume is optional. One thing that is popular is to utilize dopplers primarily, but have one microwave on each approach so you can get rich count, headway, and vehicle classification data on either side of the workzone, but have dopplers as the work horses. For more specific information on sensor choice, see my posts on dopplers and microwave sensors