# Dynamic Low-Emission Zones for Urban Mobility: A Systematic Review
## 4 Results
### Pricing Strategies
#### 4.2.1 Electronic Road Pricing System for Low-Emission Zones to Preserve Driver Privacy [18]  
This study introduces an innovative electronic road pricing (ERP) system designed explicitly for LEZs to balance the need for fraud control and driver privacy. The proposed system utilizes cryptographic mechanisms and revocable anonymity to ensure that only fraudulent drivers lose their privacy while honest drivers remain anonymous. Its key contributions are follows:  
* Revocable Anonymity: Honest drivers retain complete anonymity, while fraudulent drivers are identified through revocation mechanisms when they fail authentication or proper payment.
* Tamper-Proof Secure Elements (SEs): Each vehicle is equipped with a secure element to perform sensitive operations, ensuring the integrity of entrance and exit proofs.
* Dynamic Fee Calculation: Prices are calculated based on vehicle category, emission levels, and time spent within the LEZ, promoting equitable and environmentally sensitive tolling.
* Fraud Control Mechanisms: Checkpoints use cryptographic proofs and take photographs only in cases of authentication failure, ensuring fairness and accuracy in fraud detection.
* Privacy Preservation: The system ensures that vehicle itineraries cannot be reconstructed, and each entrance and exit process generates unique encrypted credentials, preventing traceability.
* Scalability and Efficiency: The protocol supports real-time interaction between vehicles and checkpoints, making it practical for deployment in busy urban environments.  
This ERP system is directly applicable to dynamic LEZ implementations, where real-time data and privacy preservation are critical. Its combination of fraud detection, privacy, and dynamic pricing offers a robust framework for adaptive LEZ strategies, enabling efficient traffic management and emission reduction.  
2.2 Collaborative Road Pricing Strategy for Heterogeneous Vehicles Considering Emission Constraints [27]  
This study presents a bi-level collaborative road pricing strategy for heterogeneous traffic, incorporating congestion and emission tolls. The approach targets two vehicle types: conventional vehicles (CVs) and new energy vehicles (NEVs), treating them as distinct categories with specific tolling mechanisms. The strategy integrates traffic management and environmental considerations, focusing on mitigating congestion and reducing emissions in Low-Emission Zones (LEZs). Its key contributions are as follows:  
* Bi-Level Optimization Model: A bi-level programming framework simultaneously optimizes travel efficiency and emission reduction. The upper-level model minimizes total travel time and emissions, while the lower-level model ensures equilibrium in multi-modal transportation networks.
* Distinct Tolling Mechanisms: CVs pay both congestion and emission tolls, while NEVs only pay congestion tolls, encouraging the adoption of cleaner vehicle technologies.  
Real-World Case Study: Conducted within the Second Ring Road of Beijing, the strategy achieved a 5.04% reduction in total travel time and a 10% reduction in LEZ emissions, with overall network emissions reduced by 2.04%.
* Dynamic Impact Analysis: Explored the effects of varying NEV penetration rates and emission constraints, demonstrating that a balanced NEV penetration rate of 20-30% maximizes network efficiency while meeting emission targets.
* Collaborative Tolling Benefits: Compared to standalone congestion or emission pricing, the collaborative approach significantly improves traffic flow distribution and environmental outcomes, highlighting the synergistic benefits of integrating both pricing strategies.  
A comprehensive framework for dynamic LEZ management is described, incorporating real-time data to adjust tolls based on traffic and emission metrics. The bi-level optimization and focus on heterogeneous traffic types align closely with the objectives of adaptive LEZ systems.