**One-Way Roads: Part Two**

In a series of posts starting

here, I began discussing the requirements for one-way roads, how they behaved in real life, and what ideal settings for them would be in a traffic simulator that did not conflict with the NWM. Based on a number of factors, I had originally proposed an increase of 50% of both speed and capacity for these roads. After some discussion, I decided to make an initial release using a 30% increase to see if that would be sufficient. All my tests showed that it wasn't by a significant amount; furthermore, I received no feedback from anyone to the contrary based on experience with this release. As a result of my own tests, further research, and a lack of feedback to the contrary after the initial release, I changed the increase of speeds and capacities over standard roads to 50% with the release of

Simulator Z v2.0. I would like to explain the additional factors in making this choice.

First and foremost, the 30% increase was much smaller than that experienced in corresponding one-way roads, and just did not make enough of a difference. The "intrinsic" advantage of one-way roads over two-way roads in SC4, due to the fact that volume is computed on a per-commute cycle basis and congestion is computed on a per-day cycle, turned out to be low to nonexistent in the most common cases. Furthermore, with one-way roads, the distance traveled by Sims is often a little bit longer, as they often have to travel extra either at the beginning or end of their journey on a one-way road. This also tended to cancel out any intrinsic advantage these roads had, and in some circumstances, would make trips using them slower than trips using two-way roads of equivalent speed and capacity.

I had mentioned earlier that capacity and speed increases in the real world for one-way roads were generally rated in the 67% to 75% range; Maxis used a 100% capacity increase with no speed increase, which is more or less equivalent to this. I remember playing the vanilla game with the Maxis numbers, which seemed fairly realistic, and not that far off ideal. They would reduce congestion significantly in an area, but if traffic were really bad, these roads could easily get congested themselves. This seems to be proper behavior for one-way roads. From this point of view, a 50% increase is definitely on the conservative side. These numbers all correspond in real life to one-way roads with timed lights, which produce the "green wave" that Alex described earlier.

I also found a smaller set of references describing a smaller set of speed increases for one-way roads. Upon closer examination, these appeared to be for what we would call streets in SC4. In these examples, there were no timed lights, and the road width was small. These would be best served in SC4 by one-way streets, which would have the speed and capacity of regular streets. It is my understanding that construction of such streets is possible, and I would urge some interested and capable party to create them. In the mean time, their position can be filled by regular streets or one-way roads, depending on the situation.

A big point has been the question, How suitable is this for NWM? Again, looking at the real world, it would seem to be even more important for NWM than for regular roads. Wide one-way roads almost always come with timed lights, and thus enjoy the full 67% to 75% capacity and effective speed increase described above.

One reason I chose the 50% speed increase is that it works out very well for fast avenues, which are typically found in suburban and exurban areas. Right now, these avenues would have to be built by hand out of one-way roads, but the NWM project might be interested in constructing full-blown versions of these avenues, as a new speed tier would be very useful in the settings I mentioned. A 50% increase would mean that in Simulator Z, instead of a speed of 50 kph (31 mph) for cars, fast avenues would have a speed of 75 kph (46 mph). Suburban and exurban avenues typically have a speed of 40 mph (65 kph) to 50 mph (80 kph). Although 75 kph appears to be on the higher side of this range, a closer look show that it's not. Higher speed avenues, especially on the upper end of the speed range, tend to have stoplights placed farther apart, and this tends to raise the average speed on these avenues compared to the speed limit, especially in comparison with city avenues. So this makes the 75 kph speed much more in the middle or even lower part of this range, depending on the avenue. (We also have to remember that SC4 speeds do not correspond exactly to RL speeds; it is the ratio that is important here.) Therefore, the 50% increase seems ideal for creating fast avenues, and I would urge the NWM folks to seriously consider this as an alternative avenue type. In the mean time, users can create such fast avenues themselves.

Is there a possibility for abuse here? Of course! Players can cheat in many ways, and this will introduce yet another. It is impossible to prevent cheating. Yet when used as intended, these higher speed one-way roads are not cheating at all, and merely represent a better representation of real-life traffic. Since that's what the traffic simulator is trying to do in general, it seems quite appropriate to use them.