The Gen3 car was launched without a conventional rear braking system, as the regeneration at the rear axle offered enough stopping power to slow the cars down for each corner.
Concerns over the off-season about the braking, manifested by incidents for Sam Bird and Sebastien Buemi during private and collective testing respectively, have expedited the introduction of an emergency system for the Diriyah round.
The hydraulically-operated emergency braking system operates via a solenoid valve system that can be triggered in the case of a powertrain failure, allowing the driver to stop the car in that event.
Small brake discs and calipers have been added to the rear axle of each car, and has been designed as a single-use system to provide a safety net to prevent any large crashes - particularly on the cast of street circuits used in Formula E where run-off is at a premium.
Jaguar Formula E sporting director Gary Ekerold explained the operation and the logistics in introducing the system.
"As an additional safety precaution, the championship has decided to add a hydraulic rear brake system to the car, which is only allowed to be used in certain circumstances," Ekerold told Autosport.
"It's an emergency feature, which is activated by the team software given a set of certain circumstances and criteria. When the system identifies that there's no regen on the car and a certain amount of front brake pressure has been applied, it activates the rear brake."
These discs are designed to be used once and, in the event that they have to be activated at high speeds, the damage to the disc and hardware means that the car cannot continue to run.
Ekerold explained that, although a low-speed activation could result in minimal damage to the components at the rear axle, the use of the emergency brake will ultimately result in a driver's result from that race being disqualified.
"It is fundamentally a one-use system in the sense that the assumption is that your powertrain has failed by the time you need to activate it, so you're effectively out of the race anyway," he said.
"The way that it's been designed, and because it's a retrofit, it doesn't have a floating disc. It has a fixed disc, and obviously when the caliper closes on it, it does damage the disc slightly.
"If you use it at a very high speed, it will damage the hardware on it, so it has to be replaced. At low speed, you can get away with it and you could reset it and continue. So there's been a debate about what happens when you activate the system.
"The conclusion we've come to is that, during a free practice session, like you have with any damaged component on the car, you come back to the pit and your team assesses the viability and safety of the car. If they deem it safe, you can continue. In qualifying if it happens, you'll be excluded from qualifying - and in the race if it activates, you'll be excluded from the race."
Although it could be perceived as a harsh punishment, the emergency brakes are considered a safety device like a halo.
Should a halo become damaged during the course of a race, the car could be theoretically fine to continue in a mechanical sense, but the damage to that mandatory safety device would result in that car having to retire.
The emergency brakes were not ready for action in Mexico, and thus the decision was made to extend the run-off into heavy braking zone like Turn 1 - where the full length of the straight left without a barrier to allow the cars to slow down.
However, Formula E's management and the teams involved had pushed for an earlier introduction for the system, which had been due to be introduced in Sao Paulo - the fifth round of the championship.
This means that spares are limited for the Diriyah round, but Ekerold is confident that everyone will have enough braking materials regardless.
The race in Mexico showed that teams could run a full race distance without encountering any issues with stopping the car, and that adding the emergency system onto the car is purely a "belt and braces" measure.
"Different teams carry different levels of spares - although we have got a challenge here this weekend and that because it's been introduced for the first time, our spares are pretty limited," Ekerold continued.
"But in any set of circumstances, you would be able to replace the discs if you damage them. The challenge we've got is if somebody activated it and the disc is slightly compromised - you can't take the system off the car because you have a sporting equity exercise here where you are adding ballast to the rear of the car.
"These cars were designed to be safe and to operate without that system in place. This is just a belts and braces exercise, to mitigate some people's concerns whose risk profiles are slightly different from other people's risk profiles.
"That's not to say that one is right and one is wrong. But you do have to take those people's concerns into consideration when you are doing this."
Ekerold praised Formula E and the FIA's technical staff for getting the system in earlier than planned and, although he explained that the number of braking incidents in testing was relatively small, it was enough to get the roll-out of the system fast-tracked.
"It would've been Sao Paulo that we would've got it in, and there's that four-week gap between Cape Town and Sao Paulo that most of that activity would've happened.
"I think they felt that there wasn't enough time between these events that are happening every two weeks now to get a system like that in place.
"But fair play to them, they've done a good job and they've pulled it out of the bag to get the hardware to us nearly four races earlier.
"The FIA, Formula E and all the teams are super conscious of safety in this championship. That is highest on their priority level. It's just that, with one or two incidents, it's scared one or two people.
"And you can debate whether it was right or wrong. All the drivers got out of the cars, no drama, nobody was hurt - these cars are very, very safe cars."
