Average daily traffic and percentage of truck traffic - Higher truck traffic may warrant a higher test level.

Type of roadway (interstate/county road, divided/undivided, one-way/two-way traffic) - Type of roadway can help determine traffic mix, type of end treatment needed, and potential long term maintenance concerns.

What is located under or adjacent to the bridge (lower roadway, water, schools, and emergency services)? The T631 and T631 LS rail cannot be used over lower roadways.

Posted speed at the bridge - Speeds above 45 mph require a TL-3 or higher test level rail.

Approach roadway width, horizontal and vertical alignment, and grade - Horizontal and vertical curves can increase the potential for rail impact. Another concern is the potential for narrowing of the approach roadway at the bridge location.

Bridge overall width, shoulder width, horizontal and vertical alignment, and grade - Horizontal and vertical curves can increase the potential for rail impact.

Pedestrians - Pedestrians require a taller rail. Refer to Chapter 3, "Pedestrian, Bicycle, and ADA Requirements for Bridge Railing," and Appendix B, "Acceptable Placement of Bridge Railing for Vehicular and Non-vehicular Traffic" for more information.

Drainage -

If the bridge may overtop within the hydraulic design requirements, consider using a rail categorized for drainage.
For drainage of the bridge slab,
If water is allowed to drain off the bridge slab, then consider using a rail categorized for drainage or using slots in the rail. Drain slots should not be placed over railroad tracks, lower roadways, or sidewalks. For rails that are used as separator rails between traffic and pedestrians, do not use drain slots in the separator rail to reduce the potential for ponding on the sidewalk.
If the water has to be collected, consider using a rail with a solid concrete parapet or curb.

End treatment - Is there enough distance to install MBGF to the required lengths or will a crash cushion be needed? The T631 and T631LS rail have specific MBGF lengths needed to anchor them, as identified on the standard details. Many crash cushions require a concrete barrier to anchor to and needs to be taken into consideration.

Maintenance - The different rail types will require different levels of repair when impacted. The T631 and T631LS will need to be replaced. Predominately steel rails similar to the T1W tend to need more extensive repairs after an impact than solid concrete rails like the T221. Maintenance concerns need to be considered but should not be the only deciding factor. Maintenance concerns should not override drainage or open rail needs and be considered along with other aspects, such as a community's desire for an aesthetic rail and the need for a historic looking rail.