This paper describes a radio architecture and circuit implementation results for Korea/Japan standards of 5.8GHz DSRC systems. By characterizing specific system features concerning practical environments such as communication cell area and in-vehicle temperature, we extract detailed design specifications and show a practical system implementation. Also, we introduce a new receiver sensitivity control method which has superior signal quality over the conventional ones by gating the detected RX data with respect to the received RSSI, without degradation of receiver SNR. When the complete transceiver circuit is integrated on a chip using 0.18um CMOS technology, the transmitter carries up to +10.5dBm of output power and the receiver has less than 17dB of system noise figure. The active current consumptions are 102mA and 52mA during TX- and RX-modes, respectively, for 1.8V supply voltage.