Drivers across Northern California are inundated with roadside messages -- everything from billboards to calls to action. Among them, a directive to call 911 to report drunken drivers.However, few of those drunken drivers calls end in arrest, and in one woman's case, the lack of response haunts her. On Feb. 22, driver Dierdra McElroy jumped on to Highway 99 en route to Lodi from Lathrop and almost immediately found a driver who had trouble staying in her lane. "I noticed a car that was causing problems like we all notice in the traffic. So I moved over into the left lane -- there's only two lanes -- and that car had its right-turn signal on and it suddenly tried to change lanes, literally ran this poor guy in a little black sedan out of his lane completely," she recalled. "He managed to avoid her and then she went back in her lane and he went back in his lane I was like, 'Oh wow.'"McElroy gave the driver the benefit of the doubt, believing it was probably just a bad lane change. However, the poor driving continued. "Then, I realized when she left her lane completely into the median, it was kicking up rocks, that something was really wrong and it just got worse from there," she said.McElroy thought it best to pass the driver in what appeared to be a silver Ford Escape. Then, she pulled up beside her. "She was -- had a cigarette with her arm out the window, was slumped and her eyes were very hooded, and just something was really wrong," McElroy said.With those roadside reminders in mind, she called 911. KCRA 3 obtained each of the four 911 calls McElroy made over the next 22 minutes. "She has almost run off the road. Almost hit -- sideswiped several people. She's going 30 miles per hour and then 80," McElroy said in her first 911 call.The dispatcher asked McElroy for the SUV's license plate number and what kind of car it was, and told McElroy that someone would respond.The California Highway Patrol, however, would not catch up to McElroy and the driver of that SUV before McElroy would call again -- six minutes later -- as the driver lost control."911 emergency. What are you reporting?" the dispatcher asked during the second 911. "I just called about a lady that has something really wrong with her driving, and she just hit someone," McElroy said in a panic. Video shows the SUV moved into the right lane and hit an 80,000-pound tanker belonging to Aslan Cold Storage, LLC. The force of the impact apparently wasn't enough for the tanker driver to realize they'd been hit. Neither driver of the tanker or the SUV stopped. Both continued their travel.The call continued with McElroy telling the dispatcher she'd already called about the driver. "Did you get a plate number by chance?" asked the dispatcher. "Um, I reported it the first time," she replied. "You report -- so you called this in already?" said the dispatcher. "I did, but nobody's coming, and she's gonna kill someone."McElroy called again as the driver exited Grant Line Road before eventually getting back on Hwy. 99. She called a fourth time as the driver went down 47th Avenue. "She exited the freeway. We're now on 47th Avenue," McElroy is heard saying to a 911 dispatcher. "You're now on 47th? Ma'am, are you following her?" asked the dispatcher. "I am!" she replied. "Do not -- do not follow her. OK? Take all precautions for your safety," the dispatcher said. "You're not going to catch her," she responded. "I need you to stop following her. It's not safe, OK?" the dispatcher said. "But you're not going to catch her if somebody ..." McElroy is heard saying before being cut off. "We have it out to our units. Just keep taking precautions for your safety, OK?" said the dispatcher. CHP Officer Mike Harris, who saw the video, said it's clear there's something wrong with the woman in the silver SUV."There's some serious issues about her driving and her safety, and I absolutely think that she should have been apprehended, or at least stopped and talked to find out what was going on," he said.However, CHP never caught up to her that day."(McElroy's) first call was in the Stockton area and the nearest beat unit was just a little bit south of her location, tied up on a call that they weren't able to leave, and then the next unit beyond that was another 7 miles south of that," Harris explained. Harris said that because McElroy was crossing CHP boundaries, from Stockton to South Sacramento CHP, her 911 calls would cross that boundary with her. "This is the series of unfortunate events," Harris said. "The unit that was in that area was assigned to a pedestrian call on the freeway, which is a priority call over what she was witnessing on the roadway. And immediately after that call, they had a non-injury traffic collision that they had to respond to. So, as she was traveling north, the reality of these 911 calls is that they can be difficult to locate and be difficult to apprehend because they're moving and most of the time we get one call and that's it."Additionally, Harris said that because neither the driver of the SUV nor the driver of the tanker stopped following the crash, there was no victim. Without a victim, he explained, the ability of the CHP to respond to a crash scene is limited. According to numbers provided by CHP, 911 dispatchers received 1,394 calls in East, North and South Sacramento CHP, as well as Stockton and Tracy, about possibly impaired drivers from Jan. 1 to Feb. 26. Fifty-one of those calls -- or a little less than 4 percent -- ended in arrest. "I actually think that that number is fantastic. I think a 4 percent -- just under a 4 percent -- arrest rate for 911 callers is huge and that shows that we take the calls seriously and it shows that we work to apprehend and identify these parties, and when they are under the influence, we take them off the road," Harris said. When asked whether this is a staffing issue, he said it's not."We were appropriately staffed that day for the area as they are on most normal days. Just the way that this played out and the series of events, it was a perfect storm of this particular incident that made it difficult for our officer to get in position within that 22 minutes," he explained. Harris doesn't want drivers to hesitate to call 911 when they see someone driving erratically. He said McElroy's story shouldn't serve as a deterrent. "I highly encourage, and I don't want anybody to take away from this situation not to call 911 or think that calling 911 is not going to be effective because that's not the case at all," he urged. Regardless of the circumstances, McElroy said she can't get the the morning of Feb. 22 out her mind."Her passenger-side window was so shattered in a round shape that it almost looked like a passenger flew through the windshield," McElroy said. "The right side of the bumper and quarter panel were completely gone. I have no clue how she did not spin out and wreck after hitting that truck." Harris said Thursday via email that the CHP has conducted a thorough investigation and the driver has not been found. "It's just haunting me," McElory said about the incident.