2019 Michigan State Police Patrol Vehicle Test

1. Both Tahoes overheated, and the LA County Sheriff finished the job

Michigan devotes most of a page to what went wrong. During dynamics testing on 17 September 2018 — temperatures from 70°F at nine in the morning to 88°F by half past three — both the rear-drive and four-wheel-drive Tahoes went into partial power or protect mode on lap seven or eight of every run, for every driver, which limited speed and lengthened the final laps substantially. GM engineers investigated and believed the cause was malfunctioning thermal bypass valves, which control the flow of transmission fluid through the oil cooler.

Both vehicles were retested on 11 October with the valves replaced, in 46°F. The four-wheel-drive car was clean; the rear-drive car still lost power on the last lap of the third and fourth runs. The Los Angeles County Sheriff’s Department then tested both Tahoes on 25 October in 84°F, and the four-wheel-drive car overheated again in the later laps of runs three and four. GM declined further retesting until it had isolated the root cause.

The four-wheel-drive Tahoe was subsequently redeveloped and, on 24 January 2019, completed all 32 laps of the LASD dynamics course and its city pursuit course. Winter at Grattan made Michigan’s own confirmatory testing impossible, and the book states plainly that the MSP would accept LASD’s results as meeting its purchasing requirements. The two programmes that ran the 1979 national evaluation together were, forty years later, still covering for each other.

Both Tahoes do have lap times — 1:40.58 for the rear-drive car and 1:41.24 for the four-wheel-drive — and both carry the book’s own footnote referring the reader to this passage. The averages include the laps on which the vehicles went into reduced power, which is why the book footnotes them rather than omitting them.

2. Michigan disowns the phrase “pursuit rated”

In a passage worth reading twice, the book states that the term pursuit rated has been called into question because nobody fully understands what it represents, that pursuit capable is the more appropriate phrase, and that there is no sanctioning body and no specific performance criteria behind the designation. It then says outright that neither the MSP nor the Los Angeles County Sheriff’s Department has the authority or the credentials to award the term “pursuit rated” to any vehicle.

What Michigan does have is a purchasing specification, and this book prints it in full: 60 mph within 9.0 seconds, 80 within 14.9, 100 within 24.6; 110 mph within 4,838 feet and 120 mph within 8,985 feet; an average deceleration of 25.79 ft/s² across twenty 60-to-0 threshold stops; and completion of all 32 Grattan laps without major component failure. Meeting those criteria, the book says, does not certify anything — it justifies that a vehicle can do the job the MSP needs done.

3. Testing began in the 1950s — and the earlier record is corrected

This book adds a sentence that reframes the programme’s origins: the MSP began testing patrol cars in the 1950s. At that time quotations were requested from manufacturers and only the vehicle with the lowest quotation was tested, to see whether it met the purchasing requirements. Years later, when the quotations came in four dollars apart, the department decided to test every vehicle in order to select the best one.

That resolves an apparent conflict rather than creating one. The 1980 report states that the Police Patrol Vehicle Evaluation and Purchasing Program was developed in 1976, and the 1996, 1999 and 2001 books all count their annual evaluations back to a first one in 1976–77. Those are dates for the comparative programme — the one that tests everybody and scores them against each other. Testing itself, of a single lowest bidder against a pass or fail standard, is two decades older.