## 6 Challenges and Future Works
### Adoption of Electric Vehicles in SMP  
Green and sustainable issues are widely spread in shared mobility. The adoption of alternative fuel vehicles in commercial and private fleets can be one of the green issues. The authors of [127] adopted autonomous electric vehicles in the ridesharing system, while [22] is another related study that considered the CO\({}_{2}\) in the ridesharing system. There are various types of Alternative Fuel Vehicles (AFVs), such as Battery Electric Vehicles (BEVs), Fuel Cells Electric Vehicles (FCEVs), Flexible Fuel Vehicles (FFVs), Natural Gas Vehicles (NGVs), Hybrid Electric Vehicles (HEVs), and Plug-in Hybrid Electric Vehicles (PHEVs). Each type of alternative fuel vehicle has its own merits in the aspects of operation cost, emissions, lifetime, safety, range, network requirements, refuelling stations, and refuelling time. The electric vehicle is the main focus as it is one of the most popular ones among other alternative fuel vehicles. The challenges related to the combination of the ridesharing problem with the electric vehicles result in a more complex scenario to deal with. The related research of electric vehicles is limited in terms of strategy and operation. Hence, the challenge is associated with the ability to cope with a real-world situation. The incorporation of electric vehicles in logistics and transportation can be favourable in term of sustainability. In the categories of electric vehicles, it can be PHEVs, HEVs, FCEVs, and BEVs [128]. PHEVs and BEVs have the problem of range anxiety for the users as they can only charge at a charging station or at home. With the advancement of technology, HEVs and FCEVs do not have such problems in travelling as they can be refuelled with gasoline for HEVs or hydrogen fuel (FCEVs). However, HEVs still produce harmful emissions, while FCEVs is a zero-emission vehicle. Thus, FCEVs are highly anticipated and are becoming a trending research topic in sustainability as compared to other alternative fuels vehicles. In FCEVs, the cost of the produced energy is much higher as compared to the conventional vehicles on the road [129]. Due to the limited recharging or refuelling station in the early stage, the number of refuelling and recharging stations and the location for the stations to be installed should be taken into consideration. The second challenge is related to the adoption of electric vehicles. In terms of economic aspects, the cost of the conversion of conventional vehicles to electric vehicles could be an investment for commercial companies. Companies do not need to pay huge costs to renew their whole fleet to EVs because with a very marginal investment they can retrofit their current fleet to include the new alternative fuel vehicles [130]. The wide adoption of EVs among companies in the preliminary stage can stimulate infrastructure suppliers to invest in an extensive infrastructure roll-out [131]. This potential dilemma is often called the \"chicken-egg problem\" of alternative fuels or \"lock-in\", when neither party acts because it waits for the other. As the number of alternative fuel stations increases, it will urge more nations to participate in the market of alternative fuel vehicles. However, the condition might be different when it comes to private owning due to the high cost. Hence, subsidies from the government play an important role in reducing the cost and provide a great push for the growth of these green energy vehicles [132]. Apart from the price of the vehicles, the adding of the refuelling station for FCEVs or upgrading the existing natural compressed gas station is another cost in enabling the operation of sustainable vehicles. The amount of refuelling or recharging stations and the ideal location for them to be installed should be another concern in implementing electric vehicles. Regarding the operation aspects, efficient route planning with the inclusion of fuel cell vehicles plays a vital role in popularises it among the public.