## 3 Long-Term Implications: The Question of Urban Development and Sustainability
### Environmental Implications  
Cities around the world are constantly pursuing energy conservation and climate preservation (i.e., to reduce adverse environmental emissions). [PERSON] et al. [74] projected that in order to avoid the drastic climatic changes, GHG emissions must be considerably reduced. While [PERSON] and [PERSON] [75] found the transportation sector to be the primary source of emissions (14%) around the world, and as such, the sustainability problems in roadway projects should be addressed. Although, there have been various programmes, e.g., Green Highway Partnership and Greenroads [76, 77, 78], for promoting partnership and innovation in sustainable transportation planning. Recycling of pavement materials [79, 80], e.g., \(\sim\)99% in Japan [81], and the introduction of newer materials such as warm-mix asphalt [82] have increasingly become popular. However, as [PERSON] [83] commented, the impacts on the performance of pavements are still uncertain.  
The triple-bottom-line sustainability approach has also been researched, yet, the implementation of ITS as a tool for increasing sustainability of urban roadways is also uncertain. A life-cycle assessment study of [PERSON] et al. [53] on the urban South Carolina interstate found that an ITS strategy can reduce CO\({}_{2}\) emissions (992 tons over 2 years) more than five times than any of the Greenroads-recommended sustainable construction stage strategies, explained earlier. The study emphasised over the importance of ITS as a sustainability tool, especially since the fuel consumption reductions from ITS were 30 times higher than all four strategies combined over eight years of repaving. They further iterated that despite the emphasis of transportation agencies on strategies such as warm-mix asphalt (WMA) [84; 85], ITS can potentially provide higher savings. It should be noteworthy that the study did not account for the cost parameter of sustainability; nonetheless, these environmental savings were noted for the implementation of only one ITS strategy.  
Apart from the long-term implication of ITS in terms of environmental impacts, the life-cycle environmental performance of AVs in the transport system has also been investigated in the literature to a certain degree. A recent traffic simulation study by [PERSON] et al. [86] in the city of Rome (assuming 100% battery-electric AV private vehicle penetration rate and 15-year vehicle service life) projected that the GHG emissions in the 100% AV scenario can be 60% (~744 tonne CO\({}_{2}\)eq.) lower than the non-AV scenario over the 15 years period. Noise emissions are also a critical concern in modern societies with an increase in traffic levels. [PERSON] et al. [87] investigated the acoustic environment of future cities in a hypothetical scenario (100% electric AV passenger cars in Rome) using traffic simulation. They found due to the differences in propulsion noises between conventional and AV passenger cars a better utilisation of road capacity by AVs (i.e., platooning) and improved traffic flow in the AV scenario. It should be noted here that these studies only focused on the automation of private vehicles and disregarded mix-type traffic flow situations. Similarly, the mode choice patterns of passengers, ride-sharing and population growth, etc., were not considered. Future work on estimating the environmental impact of AVs can build upon the preliminary results of these studies to develop traffic simulation models utilising the real-world traffic flow data for the mix-type traffic containing origin-destination, occupancy, mode choice and speed-time-volume profiles of all vehicle types. This way the impact of AV on modern cities can be accurately estimated towards aiding long-term policy development by the relevant municipal agencies.