Traffic laws developed over time and adapted to suit changing road conditions. Before modern (automated) traffic lights were introduced, other attempts to control traffic had already been implemented, including manual signalling (i.e. police or city employees directing traffic with hand signals), road markings, signs and early attempts to control excess speed and driving under the influence of alcohol.
Traffic lights gained widespread popularity in the 1920s, and there are conflicting accounts as to how they were received by road users, and how they impacted on their behaviour. The key sticking point appears to have been how they impacted on traffic flow and congestion, however, rather than concerns that road users would not know how to respond to them. By the time modern, automated lights became widely used in cities, drivers were already accustomed to road signage and signals to control and direct traffic, so the principle was not new to them. There was, however, some concern as to whether or not they would always be obeyed by drivers - the first traffic lights were manually operated by police officers, and there would often be a second officer outside the signal box, the theory being that people may be reluctant to obey the lights without a visible police presence to enforce compliance.
The difficulties associated with relying on manual signalling to control traffic, especially in urban areas, were primarily the amount of police resources that were consumed and the impracticality of synchronising manual traffic controls across large areas. Automated lights allowed traffic engineers to synchronise signals across multiple blocks and intersections, to a greater degree of accuracy, so as to improve the flow of traffic, at least in theory. It was also argued that using well trained traffic constables and manual signalling was more efficient than an automated system, as it allowed greater flexibility and responsiveness to the actual traffic conditions at any given time. If you've ever been the only car stuck in a frustratingly long traffic light cycle in the early hours on Sunday morning, you'll probably have a fair bit of sympathy for this school of thought.
Ultimately, whether drivers viewed the introduction of traffic lights as a positive or negative seems to have been largely influenced by where, exactly, they were driving. If you were a commercial driver in Detroit you'd be fed up with inner-city congestion and may welcome this new invention that will allegedly make your journey smoother and more efficient. If you lived in my beautiful hometown of Geelong, Australia (lovingly and only half-ironically referred to as 'Geetroit') then you're more likely to find that these stupid new things make you stop when there's no cars coming in the opposite direction, where's the logic in that, and why bother following them anyway? In cities with fewer cars on the road, and in suburban areas, there were many instances of drivers simply disobeying the signal and running red lights if there was no obvious danger in doing so - this problem was addressed by redirecting police to monitor newly-installed lights until local drivers became more accustomed to them.
In "Fighting Traffic: the Dawn of the Motor Age in the New City" by Peter D Norton, the author describes the introduction of automated traffic lights in Chicago during the mid 1920s and quotes from newspapers at the time to give an idea as to the public response to this new technology:
To many Chicagoans, the coordinated signals were a magnificent fulfillment of engineering's promise. According to one report, "approbation is heard everywhere." Newspapers were "unanimous in their approval of the system" as were "police officials in the traffic department, taxicab drivers, individual car operators motormen and others"...[a]ll vehicular traffic benefitted.
On the other hand, we have these accounts following the introduction of automated traffic lights in Otago, New Zealand in 1930:
'The signals were hardly in place before a chorus of protest arose, and demand made for the return of the constable to point duty'...'a farcical contrivance...is being inflicted on the public.'
Pedestrians may also have been somewhat less enthused about the new technology - the first automated lights were designed solely to optimise the flow of vehicle traffic, and consequently the 'walk' cycles at pedestrian crossings were shorter in duration than they are today (although as anyone who lives in a major city knows, this is problem has never really left us). There were also some safety concerns for motorists as well. The first automated lights ran on a single sequence, rather than being staggered as they are today, this created an incentive to drivers to drive as fast as possible to get through as many green lights as they could before the sequence changed. Unsurprisingly, this led to an increase in car accidents and fatalities, but the problem was reduced by the switch to staggered sequencing by the late 1920s and early 30s.
If you want to know more about this topic, you might like to check out 'The Origins and Globalization of Traffic Control Signals' by Clay McShane (link here).
Other sources:
Peter D Norton, 'Fighting Traffic: the Dawn of the Motor Age in the New City' (MIT Press, 2008)
Alexander Trapeznik and Austin Gee, 'Accommodating the Motor Car: Dunedin, New Zealand 1901-30' Journal of Transport History 2017 Vol. 38(2).