Public Traffic Route Distance (PTRD). This is the minimum distance required to protect public traffic routes (see paragraph 12.16.3 for on-base roads) and other designated exposures. At this distance, damage and personnel injury is expected (see Chapter 2 for reaction effects). For HD 1.1 and 1.2, PTRD is normally 60% of IBD. For HD 1.3 and 1.4, PTRD is the same as IBD. Public traffic routes are classified as high, medium, and low traffic density. The traffic density will be averaged over a normal (non-holiday) week in terms of number of passengers during a 24-hour period. (Note: In applying criteria other than the default values given below (which are based on car (and rail) speed of 50 mph, and a ship speed of 10 mph), considerations such as the following will be taken into account to establish exposure levels: speed of vehicles, number of passengers per vehicle, protection afforded by the vehicle, variation in daily traffic levels in relation to AE activities, and seasonal traffic trends. The default value of two passengers per car may be used to estimate traffic density.)