The W-beam (A-profile) guardrail is common all over the world. A tested, approved and properly installed product causes little concern, or does it? What about SUV’s or sports cars not included in the standards? Even the “standard” car could be in trouble as the original position of the guardrail can change over time. Where are the functional limits of an ageing guardrail, where it no longer can provide the road safety features you should expect? To find out, a research project was financed by the Swedish Transport Administration. It was possible to establish several of these limits using full scale tests and it also provided an opportunity to compare initial computer simulation results of unusual test collisions with the real outcome. The results revealed functional limits when positioning the guardrail too low and/or leaning outwards. It showed how a small change in position can make a big difference in the outcome of a collision for “non-standard cars”. Poor ground conditions was tested as well as two serious types of damages. For comparative reasons, the TB32 test according to SS-EN 1317-2 is performed for all tests, but excluding measurement of working width and ASI. The “standard” guardrail with W-beam and weak sigma-shaped steel posts at 4 m spacing was used.