I know the rationale for a 5 point seat, I know the rationale for a booster, and IMO a 5 point illegal seat without TSIP compared with a legal 3 booster WITH TSIP is a draw for safety, leaning towards the booster for morals.
My commment is strictly in regards to crash test safety having read the CMVSS code pertaining to booster cushions.
First, there is no "crash standard" for a booster seat. Booster seats are regulated as to the amount of padding on the seat, the type of materials used, the instructions that come with them and the labelling on the seat itself. A booster seat does not restrain a passenger, so does not have to pass the same standards as a harnessed car seat.
The other issue, speaking strictly from a technical safety standpoint, is that there are no standards for testing TSIP. Even for 5pt harness systems like the BLVD - the seat passes the same minimum standards as every single other seat available on the US market, but because of the "head wings" EPS foam and internal testing, it is marketed as TSIP. Is it strictly speaking because of the support on either side of the head so there isn't room for the head to move before impacting the car seat? We have no way of knowing.
Add to this, that a 5pt harness inherently provides more SIP than a booster even with TSIP. That's just the nature of the 5pt harness - it distributes the crash forces over more points and more bony structures of the body. It also will keep the child in position.
Let's imagine for an instant a multi vehicle collision. You're t-boned - the situation you're hoping that the TSIP is going to provide the most protection in. (Should I mention at this point that side impact testing isn't required as part of FMVSS or CMVSS standards too?) The head wings of the parkway do a good job of keeping your ds contained and he is not severely injured after the first collision - but maybe he's unconscious.... no longer supporting himself, perhaps slack and leaning on the locked seatbelt. Then you get hit again. He's no longer in the proper position, the seatbelt is there, but no longer provides optimal protection because it's not positioned on his body perfectly....
The above scenario wouldn't have the same risks in a 5pt harness. Even if a child was unconscious, they would still be strapped in tight, the harness close to their body and still protected.
You can argue that a situation like that would never happen, or wouldn't adult passengers face the same risks... and yes, adult passengers would face the same risk - BUT, and this is a big but - you asked us which is safest for your ds. You asked for evidence that a 5pt is safer than a booster. I don't have statistics sitting around, but I think from the standpoint of this hypothetical situation, it's fairly obvious about the extra protection a 5pt is going to give.
The TSIP in the parkway isn't going to protect your ds's remaining kidney - the seatbelt is what's going across his abdomen, the seatbelt is where the risk of injury is from and from his internal organs impacting his skeletal structure in the last stage of the collision.
It seems you've already made up your mind, and I don't really care to get into the semantics this morning. But the facts about regulations are there. We know how 5pt harnesses perform in a collision. We know how seat belts work in a collision. A booster is a positioning device designed to allow the seat belt to protect the occupant as well as possible. And it does a good job for kids that are old enough and mature enough. But no matter how good a job it does, it will never be as good as a 5pt harness.
You asked for what was safest, that's what we're telling you. FWIW, I didn't vote in the poll. As a tech I'm not going to tell you to do something illegal. As a parent though, I would rather my child be in a regent at 3yrs old if no other available seat on the CDN market fit him. And you already have the husky and have been fine using it up until now... I just don't understand why all of the sudden getting a new booster changes everything. If you didn't have the booster, nothing would be changing, right?
So I just really don't see why a booster is best all the sudden. Safety wise nothing has changed from the point prior to you getting the booster and where you are now. What has changed is your interpretation of which one is safest and your comfort level with continuing to use a seat that's imported from the US. If it's wasn't a moral dillemma prior to now, why is it such a moral issue now? Is it because he's almost 4 and "old enough" to be in a booster in a few weeks?
I just honestly and truly don't understand.
At any rate, the safest option is to continue to use the husky. TSIP is not mandated and there are no standards for it. Intuitively a seat with TSIP looks like it provides more protection, but there are no tests to confirm this, and no standards to say that it's better. So my advice, would be to pretend that the parkway is no different than any other high back booster from the standpoint of making a decision. If you wouldn't put your ds in another one, don't put him in the Parkway either. A bit of extra protection around the side doesn't change whether or not your ds is ready for a booster or protected well enough in a booster. :twocents: