6. Conclusions

The results summarized in Table 10 and listed below highlight a strong correlation between the LoS and the safety level for managing hotspots along road networks and the corresponding crash risk levels, improving system quality for users. The results achieved show that, by increasing control delay throughout the entire intersection, the expected safety level for the expected annual number of crashes decreases. Conversely, when the estimated level of service increases (reducing the control delay of the entire intersection), the safety level improves (translating into a low value for the expected value of annual crashes per year). Results confirm that if a study intersection, under specific traffic conditions, and in a specific environmental and surrounding context, has a suitable and correct geometric configuration for reducing the number of conflict points during possible maneuvers, the control delay on the entire structure is reduced, and the LoS improves. This reflects indirectly, but positively, on the safety level because the expected value of the annual

Roundabout performance in terms of expected crash frequency for AADTtotal\_entering.

Transportation Systems Analysis and Assessment

Before After

Level of Service (LoS) C A A Reduction in total crashes per year 21% 16% Reduction in injury crashes per year 59% 31%

No treatment site

LoS and expected crash frequency at advanced geometric solutions.

This research aimed to identify road strategies to improve road safety conditions at rural two-lane two-way intersections with stop-control in order to identify crash risk factors that may affect the Level of Service (LoS) and the safety level of the

> Conversion to compact roundabout

17 s/veh 4 s/veh 9 s/veh

2.37 1.86 1.99

Solution No. 1 Solution No. 2

29,000 EUR 16,000 EUR

Adjustment to the Italian Standard by designing additional geometric modules

crashes decreases.

Study case Intersection D

Expected control delay of the entire intersection

Annual economic benefit in crash

Expected annual number of site-specific

crashes

savings

Table 10.

178

Figure 9.

In this chapter, a methodological process that can also be implemented in other domains was shown to calculate, manage, and reduce, through appropriate treatments, the expected crash risk level measured in terms of yearly crash frequency and Level of Service.

First of all, the procedure aimed to identify, and then manage, the hotspots on a rural road intersection network where high exposure to crash risk can be observed. It also sought to rank the hazardous sites, for which two measures of exposure to risk were suggested and assessed in line with the research presented, namely the crash rate and Level of Service in terms of control delay at the intersection area.

Of course, a safe system approach requires a fundamental cultural and ethical shift in thinking, but it is also true that the current road transport system is not as safe as it could be. However (a) if the system could be well supervised, (b) if the trend of a number of system status indicators (i.e., crash rate level, level of service, crash cost, etc.) could be carefully plotted to check their decay over time, (c) if design errors were promptly identified, and (d) if the correlations between design errors/access management and factors that cause increased exposure to crash risk were then investigated, in the event of human error or driver distraction, the resulting severity might not be as high. Obviously, system designers and system users must all share responsibility for managing crash forces to a level that does not result in death or serious injury.

It has been verified whether improvements can be achieved in terms of safety level (reduction of the number of crashes and injuries) and the quality of traffic (reduced control delay over the entire intersection) when the geometric design of existing intersections belonging to two-lane rural roads and located on a flat area does not meet the Italian Standard.

The experimental method covered two parallel trajectories that ultimately converge:


The results show that for the intersections in question, designing a single-lane roundabout according to the Italian Road Design Standard, or an intersection introducing left-turn lanes, deceleration lanes, and median-refuge islands could help to achieve this goal. Compact roundabouts are, in any case, the best solution in terms of Level of Service and safety level because they contribute to strongly reducing delay as well as crashes.

#### Conflict of interest

No potential conflict of interest was reported by the authors.

Transportation Systems Analysis and Assessment

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