At present various vehicles that operate off road on sites are exempt from having compulsory lifeguards (that is the original name for the equipment fitted to trams, old buses (like the B Type)) This generally means tipper trucks, skip trucks and concrete jiggers.
Don't assume that because a truck has the livery of a big construction company, that it is owned and operated by them. Many companies keep a flexibility in their operations by operating in livery contracts indeed one of the biggest in livery operations is National Express Coaches, with Bruces Coaches of Salsburgh(IIRC?) operating a lot of the Glasgow-London services. The big difference here though is that PCV's have, by law to display the licensed operator's registered address in 1" lettering which can be read from the nearside kerb. No such requirement for LGV's though, but some do put clear details on their trucks anyway - most of the Supermarket and retail trucks will be operated by companies like Fowler-Welch, Kuhne & Nagel, WH Malcolm, Stobart etc, most with high standards and contractual penalties for getting things wrong. But we drop down though the hierarchy as we get down to the Class 3 drivers and the rigid trucks, usually 4 axle for the maximum 20T payload (32T truck).
Get a Class 1 licence and there is regular work on scheduled trunk, and retail delivery services, its clean and you often get a nice uniform as well. Construction contracts are sporadic and move around from site to site as muck needs to be shifted, stone and tarmac delivered. naturally the regular work gets the best drivers,and best operators managing them. To plug the gaps you move down to less well managed operations, and often drivers sourced through agencies. When Joao Lopes killed for the second time in 3 years, because he refused to wear his prescribed glasses when driving, it was not at all clear who he was driving for because of how he had been employed, and it is rare for the owner/operator of the truck - who after all has provided the driver with the means to do such harm, is identified in any reports on a crash. Yet one truck back 12-13 years ago killed 2 young women on bikes, and put a third one in a wheelchair - reportedly twice with the same driver. You might question who is challenging the fitness of the operator to have an operator's licence in such cases.
A DfT study on trucks for moving building materials found that the 44T articulated tractor-trailer offered a 50% larger payload (29-30T)(ie 50% fewer trips = 50% less exposure to potential for crashing etc), did less damage to the roads, and cost less to operate than the 32T (maximum weight for a rigid) truck, but that the prime currency for site trucks was the 4-axle rigid - perhaps the worst sort of truck to run over you as the twin rear axles often pick up the victim between them like a giant mincing machine.
On incredibly lucky lady on London was knocked off by a taxi going up on the nearside of such a truck and finished up trapped in between the rear wheels. Fortunately the truck driver noticed the crash and stopped before any major harm was done.
Sally, although you do see a few large articulated trucks in the centre of the city there are very few in number. No company is going to have around £300,000 worth of equipment designed to run at 80Kph on the main trunk routes, with expensive and limited driver's time crawling around the city centre. Those sorts of loads are generally transferred to smaller vehicles or delivered directly at night or VERY early in the morning - imagine leaving the distribution centres (Bathgate, Bellshill etc) around 23.00 and a 9-10 hour driver's shift out and back, using the roads when they are so empty that you can drive 50 miles and never catch up with or be passed by another vehicle.
The main 'big truck' traffic on city streets is that associated with construction. machines are digging holes and there is nowhere to simply pile up the stuff (and it costs a lot more to put it down and pick it up again later) On one big city centre site in London I photographed a queue of at least 30 trucks from a total of 50 which were required to move around 3000T per day from the hole to a tipping location over 30 miles away around 150 loads leaving the site every day - for about 2 months. One big concrete pour required 30 trucks running continuously with 3 shifts of drivers for a long weekend.
Because the site requirements are so transient it is far too difficult and expensive to set up a rail siding or river wharf, or a portable concrete plant, and so the stuff simply goes on the road. For some cities there may be management regimes, as those which were run for the 2012 Olympics. With early-retired soldiers readily available the trucks were marshalled at holding points and dispatched to strict schedules to manage the impact on London's streets, and some materials were sent to the site by barge (1 canal barge = 4 trucks) (1 train = 50-75 trucks) but such opportunities need to be well planned in order to deliver the alternatives effectively.
Finally a word for the LCC 'safer truck' design - such trucks can be built now - like early low floor buses they have a price premium (which is perhaps why Glasgow seems to still be buying the high cabs for their refuse trucks - with the inherent danger of a lack of direct vision for people close to the side and front of the truck). Legislation went in in 1999 to make every new bus a low floor bus, and meet a target to have all buses in daily service as low floor accessible vehicles by 2020. We could in small ways deliver this through all Councils requiring their new refuse trucks and other LGV's to have low 'eye-level' driving positions unless a valid case can be made otherwise. I think that Edinburgh is already moving this way having seen some recently purchased street sweeper trucks with low level walk-in cabs. Let's see of this move can gain inertia and see low level walk-in as the order of the day.