Delivering resources to save time, lives, and money

St. Louis Arterial Management Interface (AMI)


In This Case Study You Will Learn

  1. The St. Louis Advanced Traffic Management System (ATMS) helps first responders and affected motorists deal with greatly varying incident situations.
  2. An Arterial Management Interface (AMI), was developed to give to quickly determine what appropriate signal changes to implement regardless of their working knowledge of the arterial system.
  3. The new interfaced reduced signal change response time from 30 minutes to 5 minutes.


Since 2006, The Missouri Department of Transportation’s (MoDOT) St. Louis District has operated a central signal system, which provides for constant monitoring of any of the approximately 1000 traffic signals with functional communication. Built off the foundation of their Intelligent Transportation System (ITS) freeway communication network, central signal control opened the ability of a trained user to immediately interact with a connected traffic signal controller to determine intersection status, performance and make adjustments as required.

Combined with MoDOT’s Incident Management program on regional freeways, the long-sought ability to quickly adjust for traffic diversions away from suddenly congested freeways onto connecting MoDOT arterials was finally realized.

The Challenges

As incidents occurred and mitigation efforts were attempted over the years, several shortcomings in the existing strategy became apparent:

  • The ability to interface with the central signal system to adjust timing plans required specialized skills,
  • Each incident’s mitigation strategy required unique understanding of the diverting corridor and,
  • The need to quickly respond with an appropriate timing plan to reduce dangerous freeway backups and to take advantage of an arterial diversion route’s limited capacity.

With those challenges in mind, MoDOT undertook an analysis to find a way to incorporate these needs into a product that would satisfy the mitigation needs for most every unplanned freeway incident.

TSMO Planning, Strategies, and Deployment

The St. Louis Traffic Management Center (TMC) is constantly staffed with experienced operators familiar with coordinating incident response. Their interaction with TransCore’s Advanced Traffic Management System (ATMS, which also houses the central signal system control) helps first responders and affected motorists deal with greatly varying incident situations. Understanding the serious consequences of unintended changes to a traffic signal, MoDOT does not allow non- engineering staff to adjust signals.  This responsibility has, and remains, with traffic engineers only.

Although well-staffed with traffic engineers, the St. Louis District is too large for any one engineer to be familiar with every arterial corridor. The St. Louis District encompasses  five counties with over 200 miles of freeways, and a traffic engineer will typically be assigned to only one county or part of a county for many years.  During an incident, which requires in-depth diversion route decisions be applied quickly, an experienced engineer, much less a less seasoned engineer may not have enough understanding of the local conditions to make the proper changes to the signals.

The need to quickly enact changes to signals becomes vital to providing some measure of success to an arterial diversion. Time needed to develop a diversion corridor signal timing strategy is not available during an active incident.

To overcome these shortcomings for lack of information and time, MoDOT traffic engineers requested a product with three vital features:

  1. Be quickly accessible and easily navigable to reference the affected location,
  2. Provide clear information about the potential diversion corridor options, and
  3. Reference pre-programmed signal information.

An electronic option was the only serious candidate. Those choices ranged from possible third party software packages, ATMS vendor development of a new module, or crude spreadsheets with basic information. Further investigation into other agencies possible use of a similar interface showed no efforts to the desired level of operation, but a few very basic graphical user interfaces were operational for asset management.

The Development of the Arterial Management Interface (AMI)

Building off the idea of a graphical user interface as the core navigation feature, a framework for layout of product modules was developed. The interface effort would need to incorporate several basic features to meet goals:

  • Easy selection of incident location
  • Graphical display of route options
  • Choices of timing plans available per route option
  • Timing plans pre-programmed into the controllers
  • Supporting information for the specific timing plans
  • Additional information for Incident Management contacts
  • Logging of diversion plan actions for future adjustments
  • Built-in instructions for occasional users
  • Interface navigation between features

Titled as the “Arterial Management Interface” (AMI), the product would allow an engineer who, at a minimum, has working knowledge of how to manipulate traffic signals, the ability to quickly determine what appropriate signal changes to implement regardless of their working knowledge of the arterial system.

MoDOT’s AMI was built over four stages via Request for Proposals (RFP) and developed to require no third-party software. This Interface combines the proven concepts of central signal systems, signal programming, and Incident Management into an innovative low-cost information application that greatly improves the efficiency and safety impacts of both operations.

Communication and Collaboration with other Jurisdictions

The AMI was initially developed to incorporate diversion information solely on roadways operated by MoDOT’s St. Louis District. However, many freeway diversion paths within the District are operated by other jurisdictions.  As the AMI developed through initial stages, MoDOT unveiled its capability to other jurisdictions to show how their participation in contributing information and willingness to incorporate their corridors could benefit the travelling public. When a diversion need arises, motorists are most likely to take the nearest path off a freeway regardless of jurisdiction. The need to accommodate a surge in flow is present even if the jurisdiction prefers to not have diverting traffic on their travel way.

Other jurisdictions can provide near-immediate response to the diverting traffic to be part of the overall AMI effort. For the St. Louis District, St. Charles County’s Gateway GreenLight (GGL) program (which incorporates St. Charles County’s and several municipality’s signals into one central signal system) recognized the need to contribute to this effort due to having many non-MoDOT arterial corridors impacted by I-70 and I-64 incidents. As part of the most recent AMI development phase, GGL corridors were incorporated and both MoDOT and GGL use the same AMI version to cooperatively manage freeway diversion incidents in St. Charles County.

Demonstration of AMI Implementation

A prime example of the AMI occurred on Saturday, August 26, 2017 at 1530 with a train derailment that shut down the widest interstate in the St. Louis Area at I-55 just south of I-270 in south St. Louis County. An engineer was on duty at the TMC overseeing an emergency work zone closure in another county when the incident occurred. The junior engineer, who was unfamiliar with the intricacies of the possible diversion routes around the incident, immediately opened the AMI and, within 5 minutes, implemented several pre-programmed signal plans around the closure.

Lessons Learned

Given the AMI covers the entirety of a 200-mile freeway system, the upgrades to the roadway network (typically in the form of interchange reconfigurations and diversion route changes) will require the AMI to be more regularly updated than first considered to stave off obsolescence of the timing plans. In addition, with any tool, staff use of the AMI must be learned and regularly practiced in order to respond without relearning during the critical initial moments of an incident.

Outcome and Benefit

The AMI has become a standard tool in daily TMC operations for engineers tasked with manning the signal operations shift. The process of enacting signal changes on a complex corridor that had taken up to 30 minutes can be accomplished in less than 5 minutes. Detailed benefits have yet to be compiled, but the promptness of signal plan adjustments has most certainly reduced the severity of mitigation delays.

Organizational Capability Element

    Freeway Operations
    Active Traffic Management/Travel Demand Management/Pricing

Content Type

Case Studies & Lessons Learned

Publishing Organization


Document Downloads

Issue Date