I have been playing around with Steelman's map and popping in a few routes that would jibe with the facts as we know them. To me this case could possibly hinge on the direction Cheryl's car was facing when it was captured by traffic cams at 236th St SW & 56th Ave W.
The police have said (and without reinterpreting their evasive use of English

), that Cheryl left home a few minutes after her husband who left at 6:50. They then said that Cheryl's car was seen at 236th St SW & 56th Ave W at 7:00am. It is possible that Cheryl left fairly quickly after her husband and pulled over to park on the street side on 58th Ave W. Upon preparing to leave (or straight after exiting) the car she realizes her missing work badge, texts the carpool buddy and takes off again and is captured by the traffic cam on 236th Ave SW before 7:00. It is logical that she would travel on 236th Ave SW to get to and from her parking space. So the car could be recorded going in both directions.
If her car is only seen once on the footage, I think whatever happened, happened at the streetside parking after the exchange of texts and the incident no longer involved her vehicle. Because it is also logical that the quickest route for a perp between where Cheryl's car was found and the culvert is 236th Ave SW. If her vehicle is used in the crime and transported back, to me that would involve another two passes of the intersection at 236th St SW & 56th Ave W.
Here is Steelman's map that I have adulterated with my own route musings...No offense to its creator I hope
https://www.google.com/maps/d/edit?mid=zD2inz0q5Tuk.kPG3YwIQbSU8&usp=sharing