One of the hardest parts of developing a highway safety improvement plan is deciding where
to start. At all levels of government from the smallest village up to the Federal Highway
Administration (FHWA), the available funds are exceeded by the needs. Like road surface
management, drainage, and everything else a highway department does, safety improvements
need to be prioritized to make the best use of limited resources.
Could a list of prioritized safety improvements cause problems in a lawsuit? The plaintiff’s
attorney may argue that the plaintiff encountered a hazard that deserves a higher priority than it
received. On the other hand, an ordering of priorities is a legitimate defense, if you have gone
through the planning process to set priorities. If you do not prioritize, you will not know where to
start, or defects will be fixed in a haphazard way.
Some factors that go into prioritizing safety improvements include:
Existing safety problems
Safety problems should be organized in this order:
Severity is how bad the accidents are. Probability is how often accidents can be expected to
occur in the future, usually based on the accident history of a location. If we combine severity
and probability, we can arrive at a priority. Locations with frequent, severe accidents should get
the highest priority. Infrequent, minor accident patterns can be given low priority. Infrequent
severe accidents and frequent minor accidents are in between.
In addition to accident rate, locations where severe accidents occur should get high priority.
Severity is a function of speed and the type of accident.
The risk of an injury in a crash increases with the speed squared, and the risk of a fatality is
proportional to the speed raised to the fourth power. If the impact speed of a crash is doubled,
the fatality risk is sixteen times higher, and the injury risk is four times higher. This is why it is
considered when prioritizing safety improvements.
Some accidents are more likely to result in injuries than others. These accidents are often severe:
When planning or doing work, look around for potential problems. This will help prevent
constructive notice lawsuits. It is hard to argue that you had no prior notice of a pothole if you
cleaned the drain inlet right next to it.
Traffic speeds often increase after pavement work. The number of run-off-road crashes tends
to go up after resurfacing, and since they happen at higher speeds, the crashes tend to be more
severe. Look for opportunities to address safety during the project. Roadside hazards like too-
deep ditches or fixed objects should be addressed along with the pavement. Chapter 5 covers
Combining projects can also save time and money. For inexpensive projects like sign
installations, driving to the site is a large part of the total cost. If you will be doing other work
nearby, that cost is reduced.
Sometimes, working in an area requires you to make upgrades. Sidewalks are one example.
Existing sidewalks are allowed to remain, but if you rebuild a sidewalk, you will be required to
bring it up to current Americans with Disabilities Act (ADA) standards. Improvements may also
be required if you rebuild the road next to the sidewalk.
“Bang for the buck”
It may seem heartless at first, but it often comes down to available money and resources.
Economists and highway engineers use benefit/cost ratios to determine priorities. On one side
of the equation are the benefits of the project. On the other are the improvement costs. Safety
projects are intended to reduce the number or severity of accidents. These cost reductions are
compared to the costs, such as design, installation, and maintenance.
Sometimes, a safety improvement will have accident costs of its own. A guiderail six feet away
from the edge of the road will probably be hit more often than a tree that is twelve feet away, but
collisions with a properly designed rail will be less severe than tree collisions.
An improvement will be cost effective if:
Economists include various factors involving interest rates and inflation. These factors are used
to compare the cost of an improvement today with an accident it prevents many years from now.
When you consider the costs of traffic accidents, it is easy to see that effective improvements can
pay for themselves quickly. These costs are based on NYSDOT calculations:
Putting it all together
With so many factors, prioritizing projects is not simple. Do you address the location with a high
accident rate, or the one where you will be chip-sealing this summer? Let’s say we have two
accident problems we wish to treat, but we can only afford to do one of them. One is a curve that
has had ten run-off-road accidents in the last year. The other is an intersection with ten right-
angle accidents in the same year.
Using NYSDOT’s accident reduction factors, arrow signs on curves reduce run-off-road
accidents by 34 percent, and oversized stop signs reduce intersection accidents by 19 percent.
The curve signs will probably reduce the run-off-road accidents to six or seven per year. The
oversized stop signs will probably reduce the intersection accidents to eight per year.
We also need to look at accident severity. If there are no fixed objects on the outside of the curve,
the right-angle accidents are probably more severe, so the accidents prevented by the oversized
stop signs may be more serious.
If you will be installing street name signs because of 911, it will be a good opportunity to install
oversized stop signs, since you will be doing sign work on the corners anyway.
When you prioritize safety work, document the rationale behind it. If you do not, it is hard to
prove that your plan was well considered. Courts have accepted a legitimate ordering of priorities
as a defense against liability claims. Documentation makes it easier to prove the priorities were