I'm a bit surprised that there hasn't been much mention of how the Lower Thames Crossing is
supposed to
alleviate traffic at the Dartford Crossing, which to my knowledge was the original aim of the scheme? While the LTC does definitely fulfill the purpose of a strategic corridor, it is simply not fit for purpose. Not only has it been proved in the past that new roads, especially with the aim of
alleviating traffic
were not successful in that regard and usually contributed to more congestion
on both roads, and I wouldn't be surprised if the LTC in it's current form is no different, without mentioning the environmental issues it'll cause especially since it goes over woodland, a SSSI and partly intrudes into the Kent Downs AONB!
I think a better solution would be a new High Speed line to the north branching off of HS1, since freight trains are more efficient in carrying cargo than lorries. There could be links between HS2 and this proposed High Speed line but I doubt it'll be necessary considering that HS2 to be knowledge will link up with HS1 already.
However, if we were still laser focused on providing a new road crossing, I would say that a now forgotten option, Option A14 (as a part of the options under, well, Option A) could be a better route than the one National Highways is currently opting for, since it doesn't intrude on any AONBs and such and only goes through the Green Belt. It would have bypassed the A282 and Dartford Crossing in it's entirety in a bored tunnel, coming out just south of Darenth and emerging just after Mardyke, both at fork junctions, with maps of the layout attached below, alongside an alternate configuration of the fork below Darenth so that freight traffic doesn't have to move to the right.
That being said, it would likely be quite expensive if not more expensive than Option C4, however here's the real kicker: there would be little intrusion on green belt with this forgotten option and no AONB or SSSI land would be cleared for the LTC, local traffic could use the existing Dartford Crossing with bus lanes perhaps being allocated, and would allow for the M25 for finally become the orbital motorway it has longed to be! Not even that, a comparison of the impacts both options would have in regards to Option C4 (the current option) and Option A14.
So, I have attached another image of where traffic currently goes, and comparing Option A14 to the current route chosen for the LTC, Option A14, at least in my opinion, would be far more effective at enabling flow for national traffic as well as providing the existing Dartford Crossing as a way for local and regional traffic to access those areas. Therefore, the LTC in it's current form only caters to some of the traffic that uses the Dartford Crossing, and from the looks it is Cross-Channel/Kent traffic heading up north to Essex and vice versa, so it wouldn't particularly help out in relieving the current Dartford Crossing, would just increase congestion and pollution, and has poor local/regional access, especially considering that National Highways has omitted junctions serving local traffic in Gravesend and Tilbury.
Also, the entirety of Option A14 being in a tunnel apart from when it emerges from the fork junctions would be extremely beneficial to the environment as greenhouse gas emissions can be filtered out, further reducing the impact this would have on the atmosphere. Oh, and did I mention that Option A14 could see a potential 40% reduction in traffic compared to the current proposed route of the LTC's 12%? Oh, and not to mention that Dartford and any area in the vicinity of the Dartford Crossing are facing very high levels of pollution, in fact high enough to exceed the WHO's legal limit of some greenhouse gases, like PM2.5, a substance which can cause lung problems and deadly heart attacks.
TL;DR: The current LTC is inadequate and will actually cause greenhouse gas emissions to rise in the area and will likely worsen the congestion and do little to nothing to mitigate the traffic on the existing Dartford Crossing. It will also cause a spew of environmental issues (encroaching upon Kent Downs AONB and a SSSI) and will continue to worsen pollution in the vicinity of the proposed route, the A2 and the Dartford Crossing. In comparison, Option A14 offers to reduce congestion by 40% and decrease emissions by a proposed 600,000+ tons.
Keep in mind this is only my opinion based off of the statistics and data available to me, and I will be happy to provide sources if anyone would like to do further reading on this.