the increase in a self-service gas station -- slowdown and a jump -- volition decline

According to Oil Information Center, the self-service gas station where a driver supplies with oil by himself became 7023 shops at the end time of March, 08.
Increasing by 861 shops (14%) during the 2007 fiscal year, the rate of the self-service gas station occupied to 44,057 stands all over the country became about 16%.
Although it increased for ten consecutive years in and after April, 1998 when a ban was removed on self-service by deregulation, the number of annual increases became fewer from 1206 in the 06 fiscal year. This center is analyzing it as "Volume of sales decreased by the jump of the gas price, and the volition which converts a stand into self-service has become blunt."
the increase in a self-service gas station -- slowdown and a jump -- volition decline