A four- lane undivided multilane highway ( two lanes in each direction) has 11- ft lanes and 5- ft shoulders. At one point along the highway there is a 4% upgrade that is 0.62 mi long. There are 15 access points along this grade. The peak- hour traffic volume has 2500 passenger cars and 200 trucks and buses ( no recreational vehicles), and 720 of these vehicles arrive in the most congested 15- min period. This traffic stream is primarily commuters. The measured free- flow speed is 55 mi/ h. To improve the level of service, the local transportation agency is considering reducing the number of access points by blocking some driveways and rerouting their traffic. How many of the 15 access points must be blocked to achieve LOS C?