Introduction of pedestrain traffic light

 Pedestrian traffic lights, essential components of urban safety infrastructure, coordinate pedestrian and vehicular movement through visual and auditory signals. Their development traces back to the mid-20th century, when rapid motorization necessitated standardized traffic control (U.S. Department of Transportation [USDOT], 2010). Research confirms their efficacy: signalized intersections reduce pedestrian-vehicle collisions by up to 50% compared to uncontrolled crossings (Retting et al., 2003). Innovations like countdown timers and adaptive sensors have further enhanced compliance and accessibility, as outlined in the U.S. Federal Highway Administration’s guidelines (Federal Highway Administration [FHWA], 2022). Emerging technologies, such as AI-driven systems that adjust signal timing based on real-time pedestrian density, are now being piloted to address urban mobility challenges (National Association of City Transportation Officials [NACTO], 2023). These advancements align with global efforts to create inclusive transportation networks under the UN Sustainable Development Goals.

Reference

Federal Highway Administration. (2022). Pedestrian safety guide and countermeasure selection system. U.S. Department of Transportation. https://safety.fhwa.dot.gov/ped_bike/ped_cmnity/ped_guide/ National Association of City Transportation Officials. (2023). Smart streets: Integrating technology into urban mobility. https://nacto.org/publication/smart-streets/ Retting, R. A., Ferguson, S. A., & McCartt, A. T. (2003). A review of evidence-based traffic engineering measures to reduce pedestrian-motor vehicle crashes. American Journal of Public Health, 93(9), 1456–1458. https://doi.org/10.2105/AJPH.93.9.1456 U.S. Department of Transportation. (2010). Traffic signal timing manual. https://ops.fhwa.dot.gov/publications/fhwahop08024/chapter1.htm

Redear respond + thesis summary extra draft

 The Stereolithography (SLA) technique is one of the most prominent and widely used 3D printing technologies, extensively applied across various industries, including construction (Jacobs, 1992). First developed by Hull (1986) and later commercialised by 3D Systems Inc., SLA involves selectively polymerising liquid photosensitive resin with UV light to create high-precision parts. This technology is known for its capability to fabricate components with high surface quality and fine resolutions down to the micrometre scale (Wu et al., 2016). As the most common resin-based 3D printing method, SLA is widely utilised due to its ability to produce highly accurate, isotropic, and waterproof prototypes and end-use parts (3DEXPERIENCE Make, n.d.). Professional SLA 3D printers, such as Formlabs’ Form 4, can print walls as thin as 0.2mm, with embossed and engraved details as fine as 0.1mm and 0.15mm, respectively (Formlabs, 2024a).

SLA 3D printing technology has significant potential to revolutionise the construction industry by enhancing efficiency, improving accuracy, and enabling mass customisation. Its primary advantages include faster production cycles, superior precision, and the ability to create customised designs at scale. These benefits not only address existing challenges in the construction sector, such as project delays and miscommunication but also pave the way for smarter, more sustainable building methods.

One of the most compelling advantages of SLA 3D printing in the construction sector is its ability to reduce project timelines. Construction projects often experience delays due to prolonged design and approval processes, material shortages, and inefficient workflows (Assaf & Al-Hejji, 2006). Traditional manufacturing methods require multiple steps—design → prototyping → mold machining → testing—which typically takes 4–8 weeks. In contrast, SLA 3D printing allows direct production from digital models, reducing the lead time to just 1–2 weeks (Singh & Singh, 2018).

Moreover, communication challenges frequently lead to misinterpretations of design changes, especially when relying on 2D drawings. SLA 3D printing enables architects and engineers to create highly detailed physical models, facilitating clearer communication and reducing misunderstandings in project planning (Formlabs, 2024a). For instance, Renzo Piano’s company, RPBW, leveraged SLA 3D printing to produce an architectural model in under 24 hours (Formlabs, 2024a). The latest Formlabs SLA printer, Form 4, can print models in as little as two hours, further enhancing project efficiency (Formlabs, 2024b).

Another key reason for advocating SLA 3D printing in construction is its unparalleled precision and accuracy. SLA parts have tolerances of less than 0.05mm, ensuring smooth edges and reducing defects commonly associated with traditional manufacturing methods (3D Systems, 2023). This high level of accuracy is particularly advantageous in applications requiring complex geometries, intricate detailing, and precise fitment, such as structural connectors and facade elements.

The superior resolution of SLA printing reduces the need for extensive post-processing, saving both time and resources. In traditional manufacturing, minor errors in measurements can lead to significant material wastage and cost overruns. With SLA, engineers can minimise errors early in the design phase, improving final product quality and optimising resource use.Beyond speed and accuracy, SLA 3D printing enables mass customisation, allowing construction firms to create bespoke components without additional costs. Unlike conventional production, where customised designs typically require expensive and time-consuming mold modifications, SLA printing offers flexibility in design iteration, making it ideal for customised building facades, interior elements, and modular construction components (Wu et al., 2016).

The concept of mass customisation has long been a goal in construction, as it allows architects to tailor designs to individual client needs without sacrificing efficiency. With SLA technology, construction firms can manufacture custom parts on demand, reducing excess inventory and lowering material waste.

Despite its numerous benefits, SLA is not the only 3D printing method used in construction. Fused Deposition Modelling (FDM) and Selective Laser Sintering (SLS) also offer advantages depending on cost, print time, accuracy, and material selection.

• SLS is more suitable for complex structural components, as SLS-printed parts exhibit superior mechanical properties compared to SLA (Formlabs, 2024a).
• FDM has broader material compatibility (e.g., HIPS, PP, TPE, nylon, PLA, ABS) and lower material costs ($80–$210 per litre), making it a more budget-friendly option (Wu et al., 2016).
• SLA materials, based on photosensitive resins, degrade over time when exposed to UV light, leading to yellowing, brittleness, and reduced performance, making them less durable than FDM materials (Xometry, 2023).

Therefore, choosing the appropriate 3D printing technology depends on project-specific requirements such as structural strength, durability, and budget constraints.

SLA 3D printing is poised to transform the construction industry by addressing critical challenges such as prolonged project timelines, miscommunication, and the need for customisation. Its speed, precision, and ability to facilitate mass customisation make it a valuable tool for architects, engineers, and builders. However, its limitations, particularly regarding material durability and cost, suggest that SLA should be used strategically alongside other 3D printing technologies like FDM and SLS.

With ongoing advancements in hardware, software, and materials science, SLA 3D printing is expected to drive innovation in sustainable construction practices, including reducing CO₂ emissions through material efficiency (UNEP, 2022). While its widespread adoption is still in an exploratory phase, continued research and technological breakthroughs could further enhance its capabilities, paving the way for a smarter, more sustainable construction industry.

References 

3D Systems. (2023). Stereolithography (SLA) 3D printing technology. 3D Systems. https://www.3dsystems.com/stereolithography

3DEXPERIENCE Make. (n.d.). SLA stereolithography 3D printing services. 3DEXPERIENCE Make. https://www.3ds.com/make/service/3d-printing-service/sla-stereolithography

Assaf, S. A., & Al-Hejji, S. (2006). Causes of delay in large construction projects. International Journal of Project Management, 24(4), 349–357. https://doi.org/10.1016/j.ijproman.2005.11.010

Formlabs. (2024a). 3D printing architectural models. Formlabs. https://formlabs.com/asia/blog/3d-printing-architectural-models/

Formlabs. (2024b). The ultimate guide to stereolithography (SLA) 3D printing. Formlabs. https://formlabs.com/asia/blog/ultimate-guide-to-stereolithography-sla-3d-printing/

Hull, C. W. (1986). Apparatus for production of three-dimensional objects by stereolithography (U.S. Patent No. 4,575,330). U.S. Patent and Trademark Office. https://patents.google.com/patent/US4575330/en

Jacobs, P. F. (1992). Rapid prototyping & manufacturing: Fundamentals of stereolithography. Society of Manufacturing Engineers.

Singh, R., & Singh, S. (2018). Time and cost comparison between rapid casting and conventional sand casting. Journal of Manufacturing Processes, 34, 307–315. https://doi.org/10.1016/j.jmapro.2018.04.017

United Nations Environment Programme. (2022). 2022 global status report for buildings and construction. https://www.unep.org/resources/publication/2022-global-status-report-buildings-and-construction

Wu, P., Wang, J., & Wang, X. (2016). A critical review of the use of 3D printing in the construction industry. Automation in Construction, 68, 21–31. https://doi.org/10.1016/j.autcon.2016.04.005

Xometry. (2023, December 4). 3D printing: SLA vs. FDM. Xometry. https://xometry.pro/en-eu/articles/3d-printing-sla-vs-fdm/

Edited by 02/04/2025 (Base on prof brad comment, i edited the reference list)