Underride Roundtable Experts are Looking at Front Underrun

Here are some recommendations and resources on front underrun. Progressive crush of the energy absorbing barrier which starts off “soft” for impacts with unprotected road users and the side of cars, and increases progressively to suit frontal impacts with a range of cars. We expect the rounded absorbing barrier extension to deflect both cars and VRU’s and to use the extended crush material to slow the car to a speed such that the underride guard can be effective such as our target 100 km/h. Strength and energy absorption values adopted from MUARC recommendations to give research based starting point for expert discussions.

 

Stephen Hadley
Underride Network

 

Volvo European statistics:

About 65% of collisions between trucks and cars involve the front of the truck (accident types B1, B3, B4, B5).

The most common severe accident is a frontal collision with an oncoming car (type B1). This is mainly due to the high relative speeds and significant difference in the masses involved.

An in-depth analysis of accidents involving heavy trucks and unprotected road users in urban areas showed that:

  • The front of the truck was the impact zone in 62% of the collisions.

Links to resources:

https://www.underridenetwork.org/underride-network-want-list-for-topics-at-iihs-underride-roundtable/

https://www.underridenetwork.org/why-front-underride-or-underrun-is-important/

Chalmers Car-to-Truck Frontal Crash Compatibility
http://publications.lib.chalmers.se/records/fulltext/160351.pdf

https://underridenetwork.org/wp-content/uploads/2015/06/AP-SP2-WS-on-VRU-Protection-for-HGV.pdf

 

pedestrian nosecone small

Underride Network minimum recommendations for front guard design are:

Front guards must have 3 levels of resistance; soft front for pedestrians and cyclists, middle area must be softer than the partner vehicle in crashes and able to absorb energy such as through crush, and rear area must be strong and stiff enough to resist underride and rotate high-speed vehicles away from the truck. We must extend the front guard from the truck probably 600 mm (2 feet) to give room for an 500 mm (1.6 feet) radius curve to deflect crash partners including VRU and cars. The extra 600 mm should give us 102 km/h or (63 mph) of protection which would exceed a general goal of 60 mph (100 km/h) which is an average speed for highway crashes in the real world.

 

Energy absorption: 100 kJ minimum (Engineers discuss?)

Strength minimum

Residual strength after full energy absorption, as set out below:

P1    400 Kn          P2    300 Kn           P3    200 Kn

(Engineers discuss?)
VC-Compat: the force generated by the car in an offset configuration crash is between 200 and 300 kN.

Require extending guard from truck minimum 600 mm (Increase stroke for energy absorption and allow room for minimum curved guard radius of 500 mm).
Increasing the length of the HC (HoneyComb shaped front nose underrun guard) increases the critical impact speed To 95 km/h (59 mph) with a 300 mm – length HC structure (+27%).

Scania has presented a project in 2003 with an increased front nose of 600 mm (and 250kg) that was said to be able to increase the critical impact speed from 56 to 80 km/h in a frontal car to truck crash. Scania has estimated that this speed increase could save 900 lives a year in Europe.

The advantage of a longer structure is not only that it can absorb more energy but it also reduces the optimum stiffness which protects smaller cars and it is important that the truck is not stiffer than the car as the crush would occur first to the weaker crumple zone and the truck nose must deform before the car to maintain advantages of the increased energy absorption.

Require the guard to be curved with a radius of 500 mm and sloped to direct cars and pedestrians away from truck.
The aim would be to provide a glance-off effect for small overlaps in compromise with a good energy absorption for big overlaps.

Soften front to lesson head injuries and increase VRU compatibility.

Height from road not to exceed 350 mm.

Full width of the front of the truck.

Other recommended associated improvements:

Wider and lower windscreen to improve direct visibility.

Pedestrian flashing and audible warnings when turning.

Object, vehicle, and pedestrian detection 360 degrees.

Blind spot camera technology along with improved convex mirrors.

 

Monash MUARC Front Energy absorbing barrier Recommendations from:
REVIEW OF TRUCK SAFETY:STAGE 1: FRONTAL, SIDE AND REAR UNDERRUN PROTECTION

A stroke equal to the maximum possible without leading to impacts on the steering wheels or axle and preferably 500 to 600mm.

A road clearance of not more than 350mm.

Full width out to the outer edge of the tyres or mudguards.

An energy absorption capacity of 100kJ.

A frontal projection of at least 300mm to provide a buffer space in impacts with the sides of cars, and hence reduce the opportunity for direct head and body contact.

Curved at the ends to reduce concentrated loads being applied in angled collisions.

A layer of progressive crush material applied to hard surfaces.

Progressive crush of the energy absorbing barrier which starts off “soft” for impacts with unprotected road users and the side of cars, and increases progressively to suit frontal impacts with a range of cars.

Residual strength after full energy absorption, as set out below:

P1    400 Kn          P2    300 Kn           P3    200 Kn

 

AP SP2 WS on VRU Protection for HGV small

Sven Faßbender, IKA, Aachen, Germany

https://underridenetwork.org/wp-content/uploads/2015/06/AP-SP2-WS-on-VRU-Protection-for-HGV.pdf

 

 

 

Moving guards away from the truck body plane by 500 mm or more  increases effective crash speed to our recommended 100 km/h for high-speed crash tests. The added  stroke distance is an easy solution for higher speed guards and high-speed public testing would encourage quick designs and working solutions. Major truck and trailer manufacturers have used this extended guard equation in their future guard designs for 20 plus years.

“The size of an energy-absorbing truck front structure directly correlates to the survivable closing speed between car and truck in head-on collisions (e.g. 75 km/h (46  mph) survivable closing-speed requires a 400 mm long energy-absorbing structure, 90  km/h (56 mph), requires 800 mm (2.6 feet)).” From Volvo Report

 

Chalmers Car-to-Truck Frontal Crash Compatibility

Increasing the length of the HC (Honeycomb shaped front nose underrun guard)  increases the critical impact speed

To 95 km/h (59 mph) with a 300 mm – length HC structure (+27%)
To 102 km/h (63 mph) with a 600 mm – length HC structure (+36%)
To 107 km/h (67 mph) with a 900 mm – length HC structure (+43%)