Core of delay calculations is just seeing how much the TTM will impact the road. To do this, one must sort out what the delay factors are (what causes the impact), delay impacts (how bad the impact is), and the overall traffic flows inherent to the location.

Delay factors include stop/go's inherent queueing and stopping, road closures requiring detours or alternate routes, lane closures inherently reducing the lane capacity of a road, TSL's slowing traffic flows and causing a time delay through the site.

Delay impacts include how long a stop/go site is (time taken between cycles), detour lengths compared to normal routes, lane capacity reduction impact on traffic flows, etc.

The first step is to determine what about your site could cause impact to traffic flows. This could be the items listed above, or could be anything else about your site. Once it is determined what is causing the delays, the next step is to determine how much they are delaying traffic.

Each basic type of delay causing TTM impact is listed below with it's calculation methods and some guidelines. For further reading, the Austroads Guide to Traffic Managmement, specifically Part 2 and Part 3 are suggested.

While some RCA's may not require delay calculations for every site, a good practice is to provide a basic outline of delay calculations where delays are expected. Avoid putting “Provided upon RCA request” or similar in your TMP as it shows you haven't considered the impact of your TTM on the road. As a TMP designer it is a part of your responsibility to ensure the traffic management you propose doesn't have an adverse affect to the road users.

Delay calculations also assist with providing guidance as to what TTM to install, and what notifications are required. If a site is expecting significant delays, it may prompt the TMP designer to put out more public notification such as VMS boards, social media notifications, and similar.

NOTE: HAS NOT BEEN CHECKED WITH REAL LIFE SITUATIONS.

Determine the AADT of each approach, specifically the traffic entering the work site

Determine the length of the site (best guideline is to use a weighted average of the furthest distance to a stop point for each approach based upon the AADT of the road).

For each stop point, use a 75th %ile queue length (refer stochastic traffic flow section in AGTM) and the site length, along with a 30km/h speed limit (adjust based upon predicted site conditions) and use this to find the cycle time for each approach.

Sum the cycle times to give an overall cycle time, and from this subtract the shortest cycle time to find the expected delay.

Using Google Maps or a similar service, determine the normal travel time between two points which crosses through your work area.

Use the same service and adjust the route to follow your detour.

Subtract the detour travel time from the normal travel time to determine the delay.

Further calculations can be done by looking at road capacities for the detour and other factors.

Lane closures cause delays with two factors, the reduction of capacity of the section of road, and the action of merging. Merging only causes delays after reaching a certain level of traffic flow, and the reduction of capacity is the same.

A general guideline is that each lane can transport 1300VPH, and merging two lanes together has a capacity of 1000VPH at the merge point.

However, if there is a queue at the merging point for any reason (poor driving behaviors, vehicle incident, poor TTM installation causing confusion) then the traffic can reach a point at which the slow merging can queue from which delays compound.