Detour Route Planning and Signing: What It Actually Takes

The gap between how a detour is bid and how a detour actually runs is one of the wider ones in this trade. On the bid it looks like a closure with signs at each end. In practice it is a second roadway that you are now partly responsible for — several miles of it, often across jurisdictions you had to get separate permission from, with devices spread out where nobody from your company otherwise goes.

This post covers the parts that determine whether a detour job makes money.

Requirements vary by state, county and city. What follows is how the process generally works and what to ask. Nothing here substitutes for the requirements of the agencies having jurisdiction over the closure and every road on the route. Verify with them, every time.

Detour, diversion, and why the word matters

The MUTCD distinguishes the two. In the 11th Edition Part 6, a detour is a temporary rerouting of road users onto an existing highway in order to avoid a TTC zone. A diversion is a temporary rerouting onto a temporary highway or alignment placed around the work area. FHWA publishes Part 6 in full at no cost.

Commercially those are different businesses. A diversion means constructing and maintaining a temporary alignment — pavement, delineation, often barrier. A detour means taking responsibility for signing and maintaining a route on roads that already exist and that other people also use. Most contract language uses "detour" loosely, so confirm which one the scope actually contemplates before pricing it.

Signing the whole route, not the two ends

The manual's guidance on detours is short and is the provision most often not met: detours should be clearly signed over their entire length so that road users can easily use existing highways to return to the original highway.

"Entire length" is doing the work in that sentence. The failure mode is signing the diversion point and the return point and leaving the middle to intuition. A driver who turns correctly at the closure and then reaches an unmarked four-way is lost, and lost drivers make U-turns in places nobody planned for. Every decision point on the route needs confirmation signing, and the route needs to work in both directions if traffic is detoured both ways.

The 11th Edition provides a DETOUR warning sign in advance of a detour over a different roadway or route, with a distance legend option, plus a broader set of guide signs for route marking. Which combination applies is an agency question — many states have detailed standard detour signing sheets, and where they exist they are what the reviewer will check against.

The jurisdiction problem

This is the part that costs schedule.

A detour around a state route closure frequently runs on city streets, county roads, or another state route. Every agency whose road carries the detour has an interest, and often a permit. The approvals run on different timelines and sometimes with different requirements — one agency may accept your standard signing package while another has its own sheets, restricted hours, or objections to routing trucks past a school.

Two practical consequences:

Establish the jurisdiction list before pricing. The number of agencies is a bigger driver of soft cost than the mileage. Our post on multi-jurisdiction permit tracking covers keeping those approvals and their conditions straight once you have them.

Assume the slowest approval sets the start date. A detour plan sitting with a third reviewer is the whole job waiting. Some agencies add a further reviewer specifically for bicycle and pedestrian provisions — MDOT SHA's utility permit general provisions, for example, require plans for all proposed road closings or detours to be submitted to the agency's Bicycle and Pedestrian Coordinator for review and comment.

What the route itself has to accommodate

A detour is a design decision, not just a signing exercise. The things that get missed:

Trucks. Commercial vehicles may need a different route from passenger vehicles because of bridge, weight, clearance, or geometric restrictions, and the MUTCD notes this explicitly. A detour that routes a loaded truck under a low structure is a serious problem and an entirely foreseeable one. Hazardous-materials traffic can require separate routing as well.

Transit. Buses often cannot be detoured the same way as general traffic, and stops on the closed segment have to go somewhere. The manual directs that provisions for continuity of transit service be incorporated into planning, including accessible temporary stops.

Pedestrians and cyclists, separately. The 11th Edition includes a combined Pedestrian/Bicyclist Detour sign and separate Pedestrian Detour and Bicyclist Detour signs for where the routes diverge, and its guidance is that bicyclists should not be directed onto the path used by pedestrians. See bicycle accommodation in work zones and pedestrian accommodation in work zones for the substantive requirements.

Emergency services and local access. Coordination with agencies having jurisdiction over affected cross streets and with emergency responders is one of the manual's fundamental principles, and it is the coordination most likely to be skipped on a job that feels routine.

Residents and businesses on the route. Not a manual requirement in most cases, but a practical one — a detour that pushes highway traffic down a residential street generates complaints that reach the agency, and the agency reaches you.

Pricing: the parts usually left out

Detours get underbid in predictable ways.

Maintenance over the duration. Devices spread across miles of public road get knocked over, stolen, turned, and buried by snow plows. Someone has to drive the route regularly and fix it. On a multi-month detour this is the largest single cost after the initial setup and it is routinely priced as an afterthought.

Inspection travel time. The route is not at the job site. Driving it is time nobody is billing to a ticket unless you set it up that way.

Device count and dispersion. A detour ties up inventory across a wide area for a long time — inventory that is therefore not available for other work. That opportunity cost is real even though it does not appear on the job's cost sheet. Our post on tracking traffic control devices by job site covers keeping visibility on stock that is not in the yard.

Replacement. Budget for losses on a dispersed route, because they will happen. See charging for damaged and lost traffic control devices for how that gets recovered, where it can be.

Revisions. Detours attract change. A complaint, an incident, or a discovered restriction produces a route revision, and revisions go back through the approval chain.

For work where the closure itself moves rather than the traffic, the economics are different again — see moving operations and rolling lane closures for that pattern, which is often the alternative an agency will consider if a detour proves impractical.

A short pre-bid checklist

• Is this a detour or a diversion, in the manual's sense?
• Which agencies' roads does the route use, and what does each require?
• Is there an agency standard detour signing sheet, and have you seen the current version?
• Does the route work for trucks, and does it need a separate truck route?
• Is transit affected, and where do relocated stops go?
• Are pedestrian and bicycle routes addressed separately, and is there a separate reviewer?
• How long must the detour be maintained, and how often will it be inspected?
• Who pays for knocked-down and stolen devices?
• What is the process and timeline for a route revision?

Most of those are questions to the agency, and asking them before the bid is considerably cheaper than discovering the answers after. If you want the ongoing side — devices tracked by location across a dispersed route, inspection visits recorded against the job — a demo will show what that looks like on a real detour.