Low-Cost Safety Improvements

The term "low-cost safety improvements" is a term that occurs more and more frequently in the traffic engineering lexicon. It also is a term that, at best, is ambiguous. After all, low-cost is relative.

To someone who deals in large projects, low cost may mean $100,000. To traffic engineers working in municipalities, where funding set aside explicitly for safety projects is often somewhere between little and none, low-cost may be equated to improving signs, changing pavement markings or simply altering a signal display at a particular location. In reality, low-cost programs may have more to do with an organization’s approach to looking for and solving crash problems than the actual amount spent on any particular improvement.

Traditionally, traffic engineering-based safety programs have followed a basic process. It involves developing a list of crash locations, assigning some ranking or priority to the locations on the list, preparing collision diagrams for those locations selected for study and then developing and implementing countermeasures to treat the highest priority locations. This process is repeated year after year and, odds are, money will run out before all the locations on any year’s list are studied, let alone treated.

In 1986, the city of Winston-Salem, N.C.’s Traffic Engineering Division decided that it would begin an annual program to find and treat crash locations and to evaluate the effectiveness of the treatments employed. Prior to 1986, there had been intermittent reviews, reports and recommendations about safety issues. However, there was no regular, ongoing effort.

The division had access to crash data in various formats. It maintained a manual file of over three years of police crash reports that were filed by location. It also had access to the state of North Carolina’s Crash Reporting System. What it lacked was a method to fund any projects.

Using the state’s crash record system, a list of candidate locations was developed. Collision diagrams were prepared for each location and as the analysis continued it became clear that many crash problems might be remedied using existing traffic maintenance workers and technicians and the supply of traffic signals, signs and markings on hand. At the time the program started, a commitment also was made to evaluate each treatment using simple before-and-after methodology.

The first program studied 50 locations and found treatments for 30. Today, and for the past several years, the program has committed to keeping at least 200 locations under study annually.

Once the program got started, it was not difficult to find candidate locations. Many emerge from the day-today interaction with the public and the other parts of the traffic engineering routine, in addition to the more traditional sources.

The ways in which traffic signals, signs and markings can be deployed to remedy crash problems is so varied that it defies developing an exhaustive list of interventions. The list below includes interventions that Winston-Salem has used repeatedly in its program.

• Creating a left-turn lane within the confines of an existing roadway;

• Adding left-turn phases to existing signals;

• Replacing yield signs with stop signs at intersections;

• Replacing two-way stops with multi-way stops;

• Installing traffic signals;

• Using bigger and/or brighter signs;

• Installing short segments of center line and stop bars at unmarked stop approaches;

• Double indicating stop signs (add a left-side sign);

• Installing the message "Stop Ahead" and "Stop" on the pavement;

• Removing signals from late night/early morning programmed flashing operation;

• Adding back plates to existing signal installations;

• Adding a signal head to an existing display;

• Replacing 8-in. signal heads with 12-in. signal heads;

• Adding "Signal Ahead" signs;

• Installing Red T displays (two red signal heads mounted horizontally over an amber and green);

• Installing an all-red interval; and

• Replacing protected/permissive left-turn phases with full protected left- turn phases.

Since its inception, Winston-Salem’s program has completed before-and-after studies at 364 locations. Each year, between 40-50 locations are added to this list. Results from these studies show the aggregate number of targeted and total crashes in the "before" and "after" periods and the percentage change. It also shows the percentage of targeted to total crashes in the "before" and "after" periods. It’s worthwhile to keep in mind that targeted crashes are the subset of total crashes that a particular countermeasure is expected to reduce or eliminate and that rarely are countermeasures evident or available to address all crashes at a location. Therefore, at any location, the change in total crashes associated with a particular countermeasure is at best proportional to the changes in targeted crashes.

As a result, the program has reduced targeted crashes by 49% and total crashes by 13%.

Low-cost safety efforts can target specific crash types and reduce their frequency. It’s worthwhile to keep in mind that these data understate the safety benefits of the program. Most of the improvements have a useful life well beyond the 3-4 years covered by follow-up studies. Consequently, they go on contributing to reduced crash activity well beyond the time period covered by the study.

The last question posed in the deck of this article is: "Do low-cost safety improvements work?"

The answer is yes. Crashes can be reduced using signs, signals and marking and everyday traffic engineering tools and techniques, especially when they are aimed at a particular type of crash at a given location. It is tempting to assume that if traffic control devices are selected and installed according to standard, then an intersection or other location is safe. In reality, there is little known about the interaction of the drivers and traffic control strategies.

The middle question in the deck asks: "How do low-cost safety improvements fit into safety efforts?"

The simple answer is they are another tool to help reduce crashes and their losses. They offer the opportunity to get beyond the traditional traffic engineering approach of simply looking at the worst locations, and they can extend the range of traditional programs.

In the medical community, there are specialists and general practitioners. Specialists see the worst cases. This is very similar to the role played by the traditional traffic engineering approach to safety. The low-cost approach seems to fit the role of the general practitioner, treating the everyday maladies. It is this role that often seems to be missing in our traffic engineering efforts to improve safety.

The first question: "What are low cost improvements?" may still be the toughest to answer. There are so many possible low-cost improvements that it’s hard to envision a complete and comprehensive list. While they generally employ traditional traffic engineering tools and techniques, nothing precludes the use of other elements of the traffic safety triangle, education and endorsement.

As stated in the opening paragraph, low-cost improvements may well have more to do with an organization’s approach to solving crash problems than the amount of money it spends doing it.