Lane closure queue length and delay calculator

This lane closure queue length calculator works hour by hour. You enter how many vehicles arrive each hour and how many the closure can carry, and it shows whether a queue builds, how long it gets in vehicles and metres, the worst wait, the total delay and how long the queue takes to clear once the lane reopens.

It answers the question every road authority, council and client asks before approving work hours: will this closure back traffic up, and by how much? It's most useful on multi-lane roads where a lane or more is closed for several hours.

How it's worked out

The calculator uses a simple deterministic queue model, one hour at a time.

1. Queue at the end of each hour = the queue at the start + arrivals − capacity, never less than zero.
2. Space per vehicle = 7 m × (1 − heavy share) + 15 m × heavy share. With 8% heavy vehicles that's 7.64 m.
3. Queue length in metres = vehicles queued × space per vehicle ÷ lanes the queue forms in.
4. Wait in minutes = vehicles queued ÷ capacity × 60. The worst wait comes from the longest queue.
5. Clearing time after reopening = queue left ÷ (reopened capacity − arrivals in the last hour) × 60. If the reopened road can't carry more than is still arriving, the queue doesn't clear.
6. Total delay (vehicle-hours) adds up the average queue across each hour, plus the time to clear at the end.

It shows the longest queue, how many vehicles it holds, the time it peaks, the worst wait, the clearing time, the total delay and the space per vehicle, with a bar chart and a table for every hour.

Real traffic arrives unevenly, platoons form at signals, and drivers divert once they see a queue. So treat the result as a planning estimate, usually a minimum for the busiest hour, and confirm capacities with the traffic management designer or the road authority.

What capacity to use

Capacity is the number that matters most, and it's the hardest to know. It depends on the speed through the work, lane widths, heavy vehicles, grades, merge layout and how close workers and plant are to traffic.

US work zone studies use about 1,600 vehicles per hour per lane as a starting value, but measured lane capacities in those studies range from about 1,200 to about 1,750. A stop/slow shuttle carries far less: one at 150 m might carry under 500 vehicles an hour each way, which you can check with the stop/slow cycle calculator.

The best source is a count from the same road. Use the TfNSW Traffic Volume Viewer and open data in NSW, or the road authority's counts elsewhere, and count on site if you can. TS 05492 says queue estimates should be based on reliable data and checked on site during the shift. Our guide to traffic counts for work zone planning explains how.

Lane closure queue length: a worked example

A crew wants to close one lane of a two-lane-each-way arterial from 2 pm to 8 pm. The designer gives a capacity of 1,200 vehicles an hour past the closure and 2,400 once it reopens. Heavy vehicles are 8% of traffic and the queue forms in one lane.

The first three hours are fine. From 5 pm the afternoon peak arrives faster than the closure can carry and the queue builds to 800 vehicles, about 6.1 km, by 8 pm. Once the lane reopens, the extra capacity clears it in about 44 minutes. Total delay is about 1,690 vehicle-hours.

The fix is obvious once you see the hours: finish by 5 pm, and no standing queue is expected at all. If the work must run later, the options are to open a lane through the peak, start after it, add a detour, or raise capacity. The detour delay calculator shows what a detour would cost drivers instead. Our guide to estimating delays from a lane closure and the one on working hours restrictions go into how authorities set permitted hours.

Vehicle lengths and state methods

This calculator uses 7 m per car and 15 m per heavy vehicle, which suits a slow-moving queue on a multi-lane road. The state methods for stop/slow and portable signal queues use different figures because they include the gap between stopped vehicles and add a safety margin:

For a short stop/slow queue in NSW, vehicles queued = arrivals per minute × stopping time, rounded up. The TS 05492 example is 45 light and 6 heavy vehicles in 15 minutes with a 3-minute stop: 9 light and 2 heavy vehicles, 120.5 m, plus 30% is 156.7 m, rounded up to 160 m. The live queue counter does that on site from a tap count.

Victorian values haven't been loaded into our tools yet, so use the method in your approved TMP.

The end of the queue is the danger

A long queue isn't just a delay. Rear-end crashes into the back of a queue are one of the biggest risks at road works. In NSW, TS 05492 now sets end-of-queue risk levels: Level 1 for urban roads up to 70 km/h, Level 2 for high-speed urban and rural roads from 70 to 100 km/h, and Level 3 for motorways and named high-risk highways such as the Hume and Newell. Each level has minimum controls.

Drivers also need to see the end of the queue: 2 × D on an open road and 1.5 × D in urban areas under Table 73. In Queensland, PREPARE TO STOP signs are measured from the predicted end of the queue, not from the controller. The end of queue planner works through those rules, and our guide to roadworks queue monitoring covers escalation on the day.

When to get professional advice

Use the calculator to compare closure times, pick the safest hours to work and explain the delay to a client. Bring in a qualified traffic management designer when:

• the result shows any standing queue on a high-speed road or motorway
• the queue would reach an intersection, a crest, a bend or another work site
• you don't have reliable traffic counts or a measured capacity
• the closure needs a road occupancy licence or permit, which usually means a TMP prepared by a qualified person

The designer's TMP and the road authority's approval decide the permitted hours. This tool helps you get there with better questions.