Autos impact radio waves
I've been heavily involved in testing outdoor public wireless LAN hotspots recently and have found some interesting values for attenuation of automobiles. The change in SNR when standing outside a car versus inside the car is often 6dB to 10dB. Iíve tested several different types of cars. Certainly take into consideration this significant level of attenuation, which will definitely impact performance and possibly the ability to associate with an access point when users are accessing wireless LANs from inside vehicles. If your wireless application must work inside specific types of cars or trucks, then perform testing to determine the attenuation of these specific vehicles.