Tesla Full Self-Driving Stymied By Larger-Than-Average Stop Signs

Electric Vehicles / 5 Comments

In this case, size matters.

Tesla has been sending out many mixed messages regarding the camera versus radar debate, but a recent discovery may prove that switching back to radar may be a better move. Tesla is doing the exact opposite, however.

In May this year, Elon Musk promised full self-driving within a year. This suggests that Tesla's current camera-based autonomous systems are good enough for hands-free driving. In June, it filed a patent for a new radar system, which indicated that Musk might be backpedaling on the previous statement.

Considering the price of Full Self-Driving recently shot up to $12,000, even on the most expensive Model S Plaid, you'd think a basic radar system would be included. As it turns out, the need for radar may be greater than ever, especially considering the discovery made by a Twitter user called Cowcumber.


Before we get to his discovery, it's worth noting that a large number of drivers using Tesla's Full Self-Driving beta have been having issues in which their cars creep slowly towards a stop sign well before the intersection. As it turns out, the reason behind this is quite simple. Tesla's equipped with the more recent camera-based system read a larger stop sign as closer and will slow down too soon.

Cowcumber tested the theory, measuring the size of stop signs in his region, and the car slowed down much sooner for the larger 48-inch sign than the 30-inch one. Other users quickly chimed in on the conversation, noting that they have the same issues, including incorrectly marking other signs as stops.

We find it slightly embarrassing that a customer made the discovery instead of Tesla's dedicated self-driving team.


According to the US Department of Transportation, there are four commonly-used stop sign sizes in America, with 24 inches being the smallest allowed. A 30-inch stop sign is the most common, used on single-lane roads and in the suburbs.

The 35-inch sign is used on multi-lane roads, while the largest (supposed to be 45 inches) is used where the driver has a limited reaction distance or if the intersection has been classified as hazardous. Larger signs are also supposed to be retroreflective to make driving at night safer.

But these signs are causing Teslas to slow prematurely, risking being rear-ended by other drivers who do not anticipate braking so far before an intersection.

Whole Mars Catalog/YouTube

The phenomenon was also captured by YouTube user Whole Mars Catalog. Around 14 minutes into the video below, you can see the car crawling toward a stop sign.

Naturally, the Teslarati were on hand to defend the camera-based system, stating that the size of the sign should not matter. According to the defenders of Full Self-Driving, the camera-based system can detect the distance as the car moves closer to the sign. The results seem to suggest otherwise, though, leaving Tesla with a bit of a problem. One hopes that it's merely an algorithmic change that's needed, but it is again highlighting the flaws of a camera-only system, which is also Toyota's favored tech.

Mercedes is one brand that disagrees. The German brand's Drive Pilot made its debut earlier this year on the S-Class and the EQS, and it's equipped with radar, LiDAR, cameras, ultrasound, and moisture sensors. But perhaps that's why Mercedes will accept legal liability for crashes caused by Drive Pilot and Tesla won't.


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