A history of accidents and their severity may warrant a roadway to be redesigned. The highway department keeps these statistics, which usually come from police reports. The type, location and severity of the accident determine what should be done.Let's say, for example, that there is a cross street that currently has a stop sign for the side road and no control on the main road. Due to the high speed and volume of the vehicles on the main road, it is difficult for drivers from the side road to turn onto the main road and lots of accidents happen. We look at what we may do to alleviate this. One option may be to put in a traffic signal at this location to control both direction of traffic. Another option may be to only allow the vehicles from the side road to turn right. Maybe another option is to put in a median "suicide" lane for vehicles to cross one direction of the main road at a time. Another example might be a 2 lane undivided highway has multiple head on collisions. This highway straight and in the middle of nowhere and some people like to go at a high rate of speed. You would think that reducing the speed is an option, but would it make a difference if drivers are not paying attention to the current speed limit? One option might be to put positive separation between the 2 directions of travel, such as median guardrail. This is the process that is used to redesign problem roadways. Sometimes, the answer is to realign the roadway. Other times, the answer is to add more traffic control measures, such as signals to the location.When designing roads, there are engineering guidelines that are used to make the roads as safe as possible. For horizontal and vertical geometry, we typically refer to state highway design manuals and the "green book" from AASHTO. For traffic control, we typically refer to the Manual of Uniform Traffic Control Devices. These guidelines are always evolving to help us design safer roads.