The Engineering Logic Behind Flared vs. Parallel Crash Barrier Terminal Ends

Road crash barriers are engineered systems where every component is critical. Yet, no component is more crucial to the system’s success—and the driver’s safety—than the terminal end.
Terminal ends, often called crash attenuators, are the specialised transition points at the beginning and end of a barrier run. They are designed to manage the kinetic energy of a vehicle that hits the barrier head-on, preventing the rigid steel from spearing the vehicle.
At McIntosh Fencing, our commitment to MASH compliance means we carefully select and install the right terminal type based on the specific site geometry. Here is the engineering logic behind the two primary configurations: Flared versus Parallel terminal ends.

A flared terminal end is positioned so that it gradually flares or curves away from the travel lane .
Where and Why They Are Used:
- Rural Roads and Verges: They are most commonly seen on high-speed rural roads where there is ample run-out distance (clear space) on the verge.
- Safety Logic: By curving the barrier away from the traffic lane, the risk of a vehicle accidentally running into the terminal end is significantly reduced.
- Impact Performance: If an errant vehicle hits the rail downstream of the flare, the geometry is already working to guide the vehicle back onto the main rail system, maximising the chance of a successful redirect.
- Critical Consideration: Flared terminals require sufficient clear roadside space. They are not suitable for locations where the flare itself would encroach upon a fixed hazard or where the available working width is narrow. The flare distance must be carefully calculated during the project design phase.

A parallel terminal end is positioned so that the end of the barrier runs largely parallel to the main traffic flow .
Where and Why They Are Used:
- Urban Highways and Narrow Medians: They are essential in constrained environments where space is limited, such as near overhead bridges, in narrow median strips, or alongside urban retaining walls.
- Safety Logic: They are designed to manage head-on impacts with a high degree of energy absorption within a very compact footprint. They do not require the lateral space of a flare.
- Impact Performance: These systems rely heavily on their internal components to buckle, collapse, or absorb the energy linearly, rather than relying on the vehicle striking the system at a gradual angle.
- Critical Consideration: Because they run parallel to the lane, the approach to a parallel terminal must be clearly marked. Due to their compact nature, they require strict compliance with MASH installation criteria to ensure the absorption elements function correctly upon impact.

Choosing the right terminal end is a highly technical decision that affects the safety performance of the entire road section.
At McIntosh Fencing, our expertise in certified installation and our ISO 9001 Quality Management System ensures correct specification and perfect installation.
Partner with McIntosh Fencing to ensure every barrier—and every terminal end—on your road network is strategically specified and flawlessly installed.













































