Parallel route detouring communication to travelers

When a roadway detour to a parallel route is needed, it is necessary to communicate the detour clearly to travelers, as well as consider the transportation safety and efficiency needs on the parallel/detour route.

Key characteristics




WSDOT regions

Other names

  • Alternate route detouring

Strategy description

When a roadway detour is used, travelers must take an unexpected, and sometimes unfamiliar, route to continue to their destination. It is important to communicate the detour clearly to all road users to ensure safe and efficient travel. Additionally, the parallel detour route will need to be prepared for this influx of additional travelers.

Pre-trip: Communicating future detour to travelers before they travel

Radio, television, and newspapers are important resources for public information and outreach, and are a great way to communicate details about upcoming work zones and potential detours to travelers. If the roadway construction will have a significant impact on travelers, providing traffic information as a news story can result in free media coverage from traditional outlets.

Web applications and social media platforms, such as Facebook and Twitter, provide an outreach mechanism that is highly accessible to many travelers without much agency investment. Social media also provide travelers with a reverse-direction outlet for reporting conditions and alerting the department of transportation. Notifications via email, text message, or smartphone push notifications can also be used to provide news of upcoming detours to travelers in the region.

Hosting public meetings gives the affected travelers, businesses, and other stakeholders information about the upcoming detour and gives them an opportunity to share feedback. Events, such as ground-breaking ceremonies, can further promote the upcoming project and associated detours.

On the road, signage and variable message signs set up before the project notify travelers of upcoming construction, lane closures, and detours. This approach has the added benefit of focusing the message to road users who currently use the route.

During trip: Communicating current detours to travelers en route

Clear signage should mark the entire length of the detour, so that travelers can understand where to take the detour, navigate the parallel route, and return to the original roadway. First, a standard detour sign should be used in advance of the detour to warn road users of the upcoming change. Additional detour signs with arrows should be installed to clearly identify the recommended path of the detour. The end detour sign indicates to travelers that the detour has ended and travelers have been routed back to the original roadway.

  • Highway advisory radio transmits audio traveler information messages to travelers within range of the radio signal. Roadside signs inform travelers of the radio frequency and often use flashing lights to alert travelers when advisory messages are being broadcast.
  • Variable message signs (VMS) can be used to publicize when a work zone will begin, traffic delays, and safety messages, such as "Slow Traffic 5 Miles Ahead" and "Right Lane Closed 5 Miles Ahead." To be most useful, VMS should provide information at key junctions giving drivers plenty of time to make an informed decision about routing.

In addition, providing updated work zone information to popular GPS navigation smartphone apps, such as Waze and Google Maps, provides customized detour information to travelers in real-time.

Parallel Route Considerations

Detours increase the amount of traffic and change the types of vehicles on the parallel route. Planning is required to ensure that the new route can handle the additional traffic load in a safe and efficient manner.

  • Signal Timing
    Parallel route volumes will increase, sometimes significantly. Often the parallel route to a freeway or other major roadway detour is an arterial, or primary roadway, through an urban or suburban area. To avoid long lines of vehicles and delay, it may be necessary to adjust traffic signal timing at individual intersections, or along an entire corridor or series of intersections.  Care should also be taken to ensure road users on side streets and private driveways are not unduly delayed as a result of the detour.
  • Pavement Preservation
    Adding large trucks or other heavy vehicles to a parallel route could impact the pavement condition, especially if that roadway typically does not carry heavy vehicles often (e.g., collector roads and neighborhood streets). If more than one detour route is available, pavement condition should be considered when deciding the most appropriate route and mitigation actions should be taken to minimize damage.

When to use this strategy

Communicating parallel route detouring to travelers make sense for work zones as well as busy roadways in corridors, urban, and suburban areas.

It works well in the following situations:

  • Full road closure
    Some work zones require a full closure of the roadway for work to be completed. In this case, a parallel route detour helps travelers navigate around the closed road.
  • Reduced-capacity work zones
    In some cases, a construction zone requires a reduction in the number of open lanes and/or narrowed lanes, resulting in significant road user delay. Recommended detours on parallel routes will encourage some travelers to take the alternative, which should reduce delays for both detoured road users and those who continue through the work zone.
  • Emergency conditions
    In response to an incident, such as a traffic collision, damage to roadway infrastructure, or natural disaster, a detour can communicate a preferred route alternative for road users.

Strategy benefits:

  • Reduced congestion and delay on both the main roadway and parallel route when travelers use a detour route
  • Complete work faster and safer with full closure and detour
  • The traveling public are more informed when they are provided with communication before their trip and en route about detours

What you need in order to implement

Policy needs:

  • Standard sign packages (for static signs and variable message signs) that adhere to established regulations

Planning needs:

  • Plan for selecting communication methods to share detour information with all affected stakeholders, including the public

Coordination needs:

  • Detours must be coordinated with the road owner agencies that will be receiving additional traffic during construction. In some cases, this will include a formal memorandum of understanding or similar agreement

Equipment needs:

  • Standard detour signs and traffic control equipment for road closures
  • Variable message signs and software for additional communication to travelers

Maintenance needs:

  • All roadside signs and equipment will need to be maintained to ensure they are operational
  • Messages must be updated regularly to match existing detour conditions, which may include covering signage on the permanent corridor to reduce confusion

Agency resources needs:

  • Staff to maintain all equipment and ensure accurate information for travelers

Learn more about this strategy

Federal Highway Administration (FHWA), Alternate Route Handbook. FHWA-HOP-06-092 (PDF).

Federal Highway Administration (FHWA), Final Rule, Work Zone Public Information and Outreach Strategies. FHWA-HOP-05-067.

About key characteristics

Location notes:

Detouring is effective for corridors with high traffic volumes that have a parallel route that could be used during an incident.

Cost notes:

Costs include variable message signs, websites, and sharing travel information with the private sector to inform travelers about travel times or delays.

Technology notes:

Some technology is needed to implement variable message signs and websites.

Collaboration notes:

Significant collaboration is required among multiple transportation agencies, emergency responders, transit agencies, and regional planning agencies to plan, design, and implement parallel route management systems.

Need or issue this strategy addresses