Aero helmets have been around in various forms for decades since they were first seen on the velodrome for the pursuit discipline. Prior to the safety restrictions introduced by the UCI in 2004 they typically consisted of a fibreglass shell designed with little if any consideration to rider safety.
Now all time trial helmets sold must meet certain safety standards that include a shock absorbent hard impact foam layer that is much the same as that of a vented road helmet.
One such design is the Chrono by LAS in Houston, Texas. The Chrono has an integrated visor, and is certified to the European safety standard CEN, and CPSC that is required for the USA - although not as stringent as the Snell. It comes in one size that effectively fits heads that measure between 54-61cm around the circumference but is clearly too small for those who normally wear a medium/large size lid. To our way of thinking the tail should have been designed to sit a little closer to the rider's back to provide minimal disturbance of air. Ventilation is conspicuous by its absence from the outside, and the removable Coolmax layer works overtime to mop up the sweat accumulated during the course of a time-trial. On the whole this helmet offers a greater level of safety than a headfairing but the shape of the shock absorbing inner shell needs refinement to suit a broader range of head sizes.